GOD'S SALVATION: LAW AND GRACE
1949 Called to beatitude but wounded by sin, man stands in need of salvation from God. Divine help comes to him in Christ through the law that guides him and the grace that sustains him:
Work out your own salvation with fear and trembling; for God is at work in you, both to will and to work for his good pleasure. [Phil 2:12-13]
THE MORAL LAW
1950 The moral law is the work of divine Wisdom. Its biblical meaning can be defined as fatherly instruction, God's pedagogy. It prescribes for man the ways, the rules of conduct that lead to the promised beatitude; it proscribes the ways of evil which turn him away from God and his love. It is at once firm in its precepts and, in its promises, worthy of love. [53, 1719]
1951 Law is a rule of conduct enacted by competent authority for the sake of the common good. The moral law presupposes the rational order, established among creatures for their good and to serve their final end, by the power, wisdom, and goodness of the Creator. All law finds its first and ultimate truth in the eternal law. Law is declared and established by reason as a participation in the providence of the living God, Creator and Redeemer of all. "Such an ordinance of reason is what one calls law." [Leo XIII, Libertas praestantissimum: AAS 20 (1887/88), 597; cf. St. Thomas Aquinas, STh I-II, 90, 1] [295, 306]
Alone among all animate beings, man can boast of having been counted worthy to receive a law from God: as an animal endowed with reason, capable of understanding and discernment, he is to govern his conduct by using his freedom and reason, in obedience to the One who has entrusted everything to him. [Cf. Tertullian, Adv. Marc, 2, 4: PL 2, 288-289] 
1952 There are different expressions of the moral law, all of them interrelated: eternal law - the source, in God, of all law; natural law; revealed law, comprising the Old Law and the New Law, or Law of the Gospel; finally, civil and ecclesiastical laws.
1953 The moral law finds its fullness and its unity in Christ. Jesus Christ is in person the way of perfection. He is the end of the law, for only he teaches and bestows the justice of God: "For Christ is the end of the law, that every one who has faith may be justified." [Rom 10:4] 
I. THE NATURAL MORAL LAW
1954 Man participates in the wisdom and goodness of the Creator who gives him mastery over his acts and the ability to govern himself with a view to the true and the good. The natural law expresses the original moral sense which enables man to discern by reason the good and the evil, the truth and the lie: [307, 1776]
The natural law is written and engraved in the soul of each and every man, because it is human reason ordaining him to do good and forbidding him to sin... But this command of human reason would not have the force of law if it were not the voice and interpreter of a higher reason to which our spirit and our freedom must be submitted. [Leo XIII, Libertas praestantissimum, 597]
1955 The "divine and natural" law [GS 89 § 1] shows man the way to follow so as to practice the good and attain his end. The natural law states the first and essential precepts which govern the moral life. It hinges upon the desire for God and submission to him, who is the source and judge of all that is good, as well as upon the sense that the other is one's equal. Its principal precepts are expressed in the Decalogue. This law is called "natural," not in reference to the nature of irrational beings, but because reason which decrees it properly belongs to human nature: [1787, 396, 2070]
Where then are these rules written, if not in the book of that light we call the truth? In it is written every just law; from it the law passes into the heart of the man who does justice, not that it migrates into it, but that it places its imprint on it, like a seal on a ring that passes onto wax, without leaving the ring. [St. Augustine, De Trin. 14, 15, 21: PL 42,1052]
The natural law is nothing other than the light of understanding placed in us by God; through it we know what we must do and what we must avoid. God has given this light or law at the creation. [St. Thomas Aquinas, Dec. praec. I]
1956 The natural law, present in the heart of each man and established by reason, is universal in its precepts and its authority extends to all men. It expresses the dignity of the person and determines the basis for his fundamental rights and duties: 
For there is a true law: right reason. It is in conformity with nature, is diffused among all men, and is immutable and eternal; its orders summon to duty;its prohibitions turn away from offense .... To replace it with a contrary law is a sacrilege; failure to apply even one of its provisions is forbidden; no one can abrogate it entirely. [Cicero, Rep. III, 22, 33]
1957 Application of the natural law varies greatly; it can demand reflection that takes account of various conditions of life according to places, times, and circumstances. Nevertheless, in the diversity of cultures, the natural law remains as a rule that binds men among themselves and imposes on them, beyond the inevitable differences, common principles.
1958 The natural law is immutable and permanent throughout the variations of history; [Cf. GS 10] it subsists under the flux of ideas and customs and supports their progress. The rules that express it remain substantially valid. Even when it is rejected in its very principles, it cannot be destroyed or removed from the heart of man. It always rises again in the life of individuals and societies: 
Theft is surely punished by your law, O Lord, and by the law that is written in the human heart, the law that iniquity itself does not efface. [St. Augustine, Conf. 2, 4, 9: PL 32, 678]
1959 The natural law, the Creator's very good work, provides the solid foundation on which man can build the structure of moral rules to guide his choices. It also provides the indispensable moral foundation for building the human community. Finally, it provides the necessary basis for the civil law with which it is connected, whether by a reflection that draws conclusions from its principles, or by additions of a positive and juridical nature. 
1960 The precepts of natural law are not perceived by everyone clearly and immediately. In the present situation sinful man needs grace and revelation so moral and religious truths may be known "by everyone with facility, with firm certainty and with no admixture of error." [Pius XII, Humani generis: DS 3876; cf. Dei Filius 2: DS 3005] The natural law provides revealed law and grace with a foundation prepared by God and in accordance with the work of the Spirit. [2071, 37]
II. THE OLD LAW
1961 God, our Creator and Redeemer, chose Israel for himself to be his people and revealed his Law to them, thus preparing for the coming of Christ. The Law of Moses expresses many truths naturally accessible to reason. These are stated and authenticated within the covenant of salvation. 
1962 The Old Law is the first stage of revealed Law. Its moral prescriptions are summed up in the Ten Commandments. The precepts of the Decalogue lay the foundations for the vocation of man fashioned in the image of God; they prohibit what is contrary to the love of God and neighbor and prescribe what is essential to it. The Decalogue is a light offered to the conscience of every man to make God's call and ways known to him and to protect him against evil: 
God wrote on the tables of the Law what men did not read in their hearts. [St. Augustine, En. in Ps. 57, 1: PL 36, 673]
1963 According to Christian tradition, the Law is holy, spiritual, and good, [Cf. Rom 7:12, 14, 16] yet still imperfect. Like a tutor [Cf. Gal 3:24] it shows what must be done, but does not of itself give the strength, the grace of the Spirit, to fulfill it. Because of sin, which it cannot remove, it remains a law of bondage. According to St. Paul, its special function is to denounce and disclose sin, which constitutes a "law of concupiscence" in the human heart. [Cf. Rom 7] However, the Law remains the first stage on the way to the kingdom. It prepares and disposes the chosen people and each Christian for conversion and faith in the Savior God. It provides a teaching which endures for ever, like the Word of God. [1610, 2542, 2515]
1964 The Old Law is a preparation for the Gospel. "The Law is a pedagogy and a prophecy of things to come." [St. Irenaeus, Adv. haeres. 4, 15, 1: PG 7/1, 1012] It prophesies and presages the work of liberation from sin which will be fulfilled in Christ: it provides the New Testament with images, "types," and symbols for expressing the life according to the Spirit. Finally, the Law is completed by the teaching of the sapiential books and the prophets which set its course toward the New Covenant and the Kingdom of heaven. 
There were... under the regimen of the Old Covenant, people who possessed the charity and grace of the Holy Spirit and longed above all for the spiritual and eternal promises by which they were associated with the New Law. Conversely, there exist carnal men under the New Covenant still distanced from the perfection of the New Law: the fear of punishment and certain temporal promises have been necessary, even under the New Covenant, to incite them to virtuous works. In any case, even though the Old Law prescribed charity, it did not give the Holy Spirit, through whom "God's charity has been poured into our hearts." [St. Thomas Aquinas, STh I-II, 107, 1 ad 2; cf. Rom 5:5] 
III. THE NEW LAW OR THE LAW OF THE GOSPEL
1965 The New Law or the Law of the Gospel is the perfection here on earth of the divine law, natural and revealed. It is the work of Christ and is expressed particularly in the sermon on the Mount. It is also the work of the Holy Spirit and through him it becomes the interior law of charity: "I will establish a New Covenant with the house of Israel.... I will put my laws into their minds, and write them on their hearts, and I will be their God, and they shall be my people." [Heb 8:8, 10; cf. Jer 31:31-34] [459, 581, 715]
1966 The New Law is the grace of the Holy Spirit given to the faithful through faith in Christ. It works through charity; it uses the Sermon on the Mount to teach us what must be done and makes use of the sacraments to give us the grace to do it: 
If anyone should meditate with devotion and perspicacity on the sermon our Lord gave on the mount, as we read in the Gospel of Saint Matthew, he will doubtless find there ... the perfect way of the Christian life.... This sermon contains ... all the precepts needed to shape one's life. [St. Augustine, De serm. Dom. 1, 1: PL 34,1229-1230]
1967 The Law of the Gospel "fulfills," refines, surpasses, and leads the Old Law to its perfection. [Cf. Mt 5:17-19] In the Beatitudes, the New Law fulfills the divine promises by elevating and orienting them toward the "kingdom of heaven." It is addressed to those open to accepting this new hope with faith - the poor, the humble, the afflicted, the pure of heart, those persecuted on account of Christ and so marks out the surprising ways of the Kingdom. 
1968 The Law of the Gospel fulfills the commandments of the Law. The Lord's Sermon on the Mount, far from abolishing or devaluing the moral prescriptions of the Old Law, releases their hidden potential and has new demands arise from them: it reveals their entire divine and human truth. It does not add new external precepts, but proceeds to reform the heart, the root of human acts, where man chooses between the pure and the impure, [Cf. Mt 15:18-19] where faith, hope, and charity are formed and with them the other virtues. The Gospel thus brings the Law to its fullness through imitation of the perfection of the heavenly Father, through forgiveness of enemies and prayer for persecutors, in emulation of the divine generosity. [Cf. Mt 5:44,48] [129, 582]
1969 The New Law practices the acts of religion: almsgiving, prayer and fasting, directing them to the "Father who sees in secret," in contrast with the desire to "be seen by men." [Cf. Mt 6:1-6; 16-18] Its prayer is the Our Father. [Cf. Mt 6:9-13; Lk 11:2-4] 
1970 The Law of the Gospel requires us to make the decisive choice between "the two ways" and to put into practice the words of the Lord. [Cf. Mt 7:13-14,21-27] It is summed up in the Golden Rule, "Whatever you wish that men would do to you, do so to them; this is the law and the prophets." [Mt 7:12; cf. Lk 6:31] [1696, 1789]
The entire Law of the Gospel is contained in the "new commandment" of Jesus, to love one another as he has loved us. [Cf. Jn 15:12; 13:34] 
1971 To the Lord's Sermon on the Mount it is fitting to add the moral catechesis of the apostolic teachings, such as Romans 12-15, 1 Corinthians 12-13, Colossians 3-4, Ephesians 4-5, etc. This doctrine hands on the Lord's teaching with the authority of the apostles, particularly in the presentation of the virtues that flow from faith in Christ and are animated by charity, the principal gift of the Holy Spirit. "Let charity be genuine.... Love one another with brotherly affection.... Rejoice in your hope, be patient in tribulation, be constant in prayer. Contribute to the needs of the saints, practice hospitality." [Rom 12:9-13] This catechesis also teaches us to deal with cases of conscience in the light of our relationship to Christ and to the Church. [Cf. Rom 14; 1 Cor 5-10] 
1972 The New Law is called a law of love because it makes us act out of the love infused by the Holy Spirit, rather than from fear; a law of grace, because it confers the strength of grace to act, by means of faith and the sacraments; a law of freedom, because it sets us free from the ritual and juridical observances of the Old Law, inclines us to act spontaneously by the prompting of charity and, finally, lets us pass from the condition of a servant who "does not know what his master is doing" to that of a friend of Christ - "For all that I have heard from my Father I have made known to you" - or even to the status of son and heir. [Jn 15:15; cf. Jas 1:25; 2:12; Gal 4:1-7.21-31; Rom 8:15] [782, 1828]
1973 Besides its precepts, the New Law also includes the evangelical counsels. The traditional distinction between God's commandments and the evangelical counsels is drawn in relation to charity, the perfection of Christian life. The precepts are intended to remove whatever is incompatible with charity. The aim of the counsels is to remove whatever might hinder the development of charity, even if it is not contrary to it. [Cf. St. Thomas Aquinas, STh II-II, 184, 3] [2053, 915]
1974 The evangelical counsels manifest the living fullness of charity, which is never satisfied with not giving more. They attest its vitality and call forth our spiritual readiness. The perfection of the New Law consists essentially in the precepts of love of God and neighbor. The counsels point out the more direct ways, the readier means, and are to be practiced in keeping with the vocation of each: 
[God] does not want each person to keep all the counsels, but only those appropriate to the diversity of persons, times, opportunities, and strengths, as charity requires; for it is charity, as queen of all virtues, all commandments, all counsels, and, in short, of all laws and all Christian actions that gives to all of them their rank, order, time, and value. [St. Francis de Sales, Love of God 8, 6]
1975 According to Scripture the Law is a fatherly instruction by God which prescribes for man the ways that lead to the promised beatitude, and proscribes the ways of evil.
1976 "Law is an ordinance of reason for the common good, promulgated by the one who is in charge of the community" (St. Thomas Aquinas, STh I-II, 90, 4).
1977 Christ is the end of the law (cf. Rom 10:4); only he teaches and bestows the justice of God.
1978 The natural law is a participation in God's wisdom and goodness by man formed in the image of his Creator. It expresses the dignity of the human person and forms the basis of his fundamental rights and duties.
1979 The natural law is immutable, permanent throughout history. The rules that express it remain substantially valid. It is a necessary foundation for the erection of moral rules and civil law.
1980 The Old Law is the first stage of revealed law. Its moral prescriptions are summed up in the Ten Commandments.
1981 The Law of Moses contains many truths naturally accessible to reason. God has revealed them because men did not read them in their hearts.
1982 The Old Law is a preparation for the Gospel.
1983 The New Law is the grace of the Holy Spirit received by faith in Christ, operating through charity. It finds expression above all in the Lord's Sermon on the Mount and uses the sacraments to communicate grace to us.
1984 The Law of the Gospel fulfills and surpasses the Old Law and brings it to perfection: its promises, through the Beatitudes of the Kingdom of heaven; its commandments, by reforming the heart, the root of human acts.
1985 The New Law is a law of love, a law of grace, a law of freedom.
1986 Besides its precepts the New Law includes the evangelical counsels. "The Church's holiness is fostered in a special way by the manifold counsels which the Lord proposes to his disciples in the Gospel" (LG 42 § 2).
GRACE AND JUSTIFICATION
1987 The grace of the Holy Spirit has the power to justify us, that is, to cleanse us from our sins and to communicate to us "the righteousness of God through faith in Jesus Christ" and through Baptism: [Rom 3:22; cf. 6:3-4] 
But if we have died with Christ, we believe that we shall also live with him. For we know that Christ being raised from the dead will never die again; death no longer has dominion over him. The death he died he died to sin, once for all, but the life he lives he lives to God. So you also must consider yourselves as dead to sin and alive to God in Christ Jesus. [Rom 6:8-11]
1988 Through the power of the Holy Spirit we take part in Christ's Passion by dying to sin, and in his Resurrection by being born to a new life; we are members of his Body which is the Church, branches grafted onto the vine which is himself: [Cf. 1 Cor 12; Jn 15:1-4] 
[God] gave himself to us through his Spirit. By the participation of the Spirit, we become communicants in the divine nature.... For this reason, those in whom the Spirit dwells are divinized. [St. Athanasius, Ep. Serap. 1, 24: PG 26, 585 and 588] 
1989 The first work of the grace of the Holy Spirit is conversion, effecting justification in accordance with Jesus' proclamation at the beginning of the Gospel: "Repent, for the kingdom of heaven is at hand." [Mt 4:17] Moved by grace, man turns toward God and away from sin, thus accepting forgiveness and righteousness from on high. "Justification is not only the remission of sins, but also the sanctification and renewal of the interior man. [Council of Trent (1547): DS 1528] 
1990 Justification detaches man from sin which contradicts the love of God, and purifies his heart of sin. Justification follows upon God's merciful initiative of offering forgiveness. It reconciles man with God. It frees from the enslavement to sin, and it heals. [1446, 1733]
1991 Justification is at the same time the acceptance of God's righteousness through faith in Jesus Christ. Righteousness (or "justice") here means the rectitude of divine love. With justification, faith, hope, and charity are poured into our hearts, and obedience to the divine will is granted us. 
1992 Justification has been merited for us by the Passion of Christ who offered himself on the cross as a living victim, holy and pleasing to God, and whose blood has become the instrument of atonement for the sins of all men. Justification is conferred in Baptism, the sacrament of faith. It conforms us to the righteousness of God, who makes us inwardly just by the power of his mercy. Its purpose is the glory of God and of Christ, and the gift of eternal life: [Cf. Council of Trent (1547): DS 1529] [617, 1266, 294]
But now the righteousness of God has been manifested apart from law, although the law and the prophets bear witness to it, the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: since all have sinned and fall short of the glory of God, they are justified by his grace as a gift, through the redemption which is in Christ Jesus, whom God put forward as an expiation by his blood, to be received by faith. This was to show God's righteousness, because in his divine forbearance he had passed over former sins; it was to prove at the present time that he himself is righteous and that he justifies him who has faith in Jesus. [Rom 3:21-26]
1993 Justification establishes cooperation between God's grace and man's freedom. On man's part it is expressed by the assent of faith to the Word of God, which invites him to conversion, and in the cooperation of charity with the prompting of the Holy Spirit who precedes and preserves his assent: 
When God touches man's heart through the illumination of the Holy Spirit, man himself is not inactive while receiving that inspiration, since he could reject it; and yet, without God's grace, he cannot by his own free will move himself toward justice in God's sight. [Council of Trent (1547): DS 1525] 
1994 Justification is the most excellent work of God's love made manifest in Christ Jesus and granted by the Holy Spirit. It is the opinion of St. Augustine that "the justification of the wicked is a greater work than the creation of heaven and earth," because "heaven and earth will pass away but the salvation and justification of the elect... will not pass away." [St. Augustine, In Jo. ev. 72, 3: PL 35, 1823] He holds also that the justification of sinners surpasses the creation of the angels in justice, in that it bears witness to a greater mercy. [312, 412]
1995 The Holy Spirit is the master of the interior life. By giving birth to the "inner man," [Cf. Rom 7:22; Eph 3:16] justification entails the sanctification of his whole being: 
Just as you once yielded your members to impurity and to greater and greater iniquity, so now yield your members to righteousness for sanctification.... But now that you have been set free from sin and have become slaves of God, the return you get is sanctification and its end, eternal life. [Rom 6:19, 22]
1996 Our justification comes from the grace of God. Grace is favor, the free and undeserved help that God gives us to respond to his call to become children of God, adoptive sons, partakers of the divine nature and of eternal life. [Cf. Jn 1:12-18; 17:3; Rom 8:14-17; 2 Pet 1:3-4] 
1997 Grace is a participation in the life of God. It introduces us into the intimacy of Trinitarian life: by Baptism the Christian participates in the grace of Christ, the Head of his Body. As an "adopted son" he can henceforth call God "Father," in union with the only Son. He receives the life of the Spirit who breathes charity into him and who forms the Church. [375, 260]
1998 This vocation to eternal life is supernatural. It depends entirely on God's gratuitous initiative, for he alone can reveal and give himself. It surpasses the power of human intellect and will, as that of every other creature. [Cf. 1 Cor 2:7-9] 
1999 The grace of Christ is the gratuitous gift that God makes to us of his own life, infused by the Holy Spirit into our soul to heal it of sin and to sanctify it. It is the sanctifying or deifying grace received in Baptism. It is in us the source of the work of sanctification: [Cf. Jn 4:14; 7:38-39] 
Therefore if any one is in Christ, he is a new creation; the old has passed away, behold, the new has come. All this is from God, who through Christ reconciled us to himself. [2 Cor 5:17-18]
2000 Sanctifying grace is an habitual gift, a stable and supernatural disposition that perfects the soul itself to enable it to live with God, to act by his love. Habitual grace, the permanent disposition to live and act in keeping with God's call, is distinguished from actual graces which refer to God's interventions, whether at the beginning of conversion or in the course of the work of sanctification.
2001 The preparation of man for the reception of grace is already a work of grace. This latter is needed to arouse and sustain our collaboration in justification through faith, and in sanctification through charity. God brings to completion in us what he has begun, "since he who completes his work by cooperating with our will began by working so that we might will it:" [St. Augustine, De gratia et libero arbitrio, 17: PL 44, 901] 
Indeed we also work, but we are only collaborating with God who works, for his mercy has gone before us. It has gone before us so that we may be healed, and follows us so that once healed, we may be given life; it goes before us so that we may be called, and follows us so that we may be glorified; it goes before us so that we may live devoutly, and follows us so that we may always live with God: for without him we can do nothing. [St. Augustine, De natura et gratia, 31: PL 44, 264]
2002 God's free initiative demands man's free response, for God has created man in his image by conferring on him, along with freedom, the power to know him and love him. The soul only enters freely into the communion of love. God immediately touches and directly moves the heart of man. He has placed in man a longing for truth and goodness that only he can satisfy. The promises of "eternal life" respond, beyond all hope, to this desire: 
If at the end of your very good works..., you rested on the seventh day, it was to foretell by the voice of your book that at the end of our works, which are indeed "very good" since you have given them to us, we shall also rest in you on the sabbath of eternal life. [St. Augustine, Conf. 13, 36, 51: PL 32, 868; cf. Gen 1:31] 
2003 Grace is first and foremost the gift of the Spirit who justifies and sanctifies us. But grace also includes the gifts that the Spirit grants us to associate us with his work, to enable us to collaborate in the salvation of others and in the growth of the Body of Christ, the Church. There are sacramental graces, gifts proper to the different sacraments. There are furthermore special graces, also called charisms after the Greek term used by St. Paul and meaning "favor," "gratuitous gift," "benefit." [Cf. LG 12] Whatever their character - sometimes it is extraordinary, such as the gift of miracles or of tongues - charisms are oriented toward sanctifying grace and are intended for the common good of the Church. They are at the service of charity which builds up the Church. [Cf. 1 Cor 12] [1108, 1127, 799-801]
2004 Among the special graces ought to be mentioned the graces of state that accompany the exercise of the responsibilities of the Christian life and of the ministries within the Church: Having gifts that differ according to the grace given to us, let us use them: if prophecy, in proportion to our faith; if service, in our serving; he who teaches, in his teaching; he who exhorts, in his exhortation; he who contributes, in liberality; he who gives aid, with zeal; he who does acts of mercy, with cheerfulness. [Rom 12:6-8]
2005 Since it belongs to the supernatural order, grace escapes our experience and cannot be known except by faith. We cannot therefore rely on our feelings or our works to conclude that we are justified and saved. [Cf. Council of Trent (1547): DS 1533-1534] However, according to the Lord's words "Thus you will know them by their fruits" [Mt 7:20] - reflection on God's blessings in our life and in the lives of the saints offers us a guarantee that grace is at work in us and spurs us on to an ever greater faith and an attitude of trustful poverty.
A pleasing illustration of this attitude is found in the reply of St. Joan of Arc to a question posed as a trap by her ecclesiastical judges: "Asked if she knew that she was in God's grace, she replied: 'If I am not, may it please God to put me in it; if I am, may it please God to keep me there.'" [Acts of the trial of St. Joan of Arc]
You are glorified in the assembly of your Holy Ones, for in crowning their merits you are crowning your own gifts. [Roman Missal, Prefatio I de sanctis; Qui in Sanctorum concilio celebraris, et eorum coronando merita tua dona coronas, citing the "Doctor of grace," St. Augustine, En. in Ps. 102, 7: PL 37, 1321-1322.]
2006 The term "merit" refers in general to the recompense owed by a community or a society for the action of one of its members, experienced either as beneficial or harmful, deserving reward or punishment. Merit is relative to the virtue of justice, in conformity with the principle of equality which governs it. [1723, 1807]
2007 With regard to God, there is no strict right to any merit on the part of man. Between God and us there is an immeasurable inequality, for we have received everything from him, our Creator. 
2008 The merit of man before God in the Christian life arises from the fact that God has freely chosen to associate man with the work of his grace. The fatherly action of God is first on his own initiative, and then follows man's free acting through his collaboration, so that the merit of good works is to be attributed in the first place to the grace of God, then to the faithful. Man's merit, moreover, itself is due to God, for his good actions proceed in Christ, from the predispositions and assistance given by the Holy Spirit. [306, 155, 970]
2009 Filial adoption, in making us partakers by grace in the divine nature, can bestow true merit on us as a result of God's gratuitous justice. This is our right by grace, the full right of love, making us "co-heirs" with Christ and worthy of obtaining "the promised inheritance of eternal life." [Council of Trent (1547): DS 1546] The merits of our good works are gifts of the divine goodness. [Cf. Council of Trent (1547): DS 1548] "Grace has gone before us; now we are given what is due.... Our merits are God's gifts." [St. Augustine, Sermo 298, 4-5: PL 38, 1367] 
2010 Since the initiative belongs to God in the order of grace, no one can merit the initial grace of forgiveness and justification, at the beginning of conversion. Moved by the Holy Spirit and by charity, we can then merit for ourselves and for others the graces needed for our sanctification, for the increase of grace and charity, and for the attainment of eternal life. Even temporal goods like health and friendship can be merited in accordance with God's wisdom. These graces and goods are the object of Christian prayer. Prayer attends to the grace we need for meritorious actions. 
2011 The charity of Christ is the source in us of all our merits before God. Grace, by uniting us to Christ in active love, ensures the supernatural quality of our acts and consequently their merit before God and before men. The saints have always had a lively awareness that their merits were pure grace. 
After earth's exile, I hope to go and enjoy you in the fatherland, but I do not want to lay up merits for heaven. I want to work for your love alone.... In the evening of this life, I shall appear before you with empty hands, for I do not ask you, Lord, to count my works. All our justice is blemished in your eyes. I wish, then, to be clothed in your own justice and to receive from your love the eternal possession of yourself. [St. Therese of Lisieux, "Act of Offering" in Story of a Soul, tr. John Clarke (Washington Dc: ICS, 1981), 277] 
2012 "We know that in everything God works for good with those who love him... For those whom he fore knew he also predestined to be conformed to the image of his Son, in order that he might be the first-born among many brethren. And those whom he predestined he also called; and those whom he called he also justified; and those whom he justified he also glorified." [Rom 8:28-30] 
2013 "All Christians in any state or walk of life are called to the fullness of Christian life and to the perfection of charity." [LG 40 § 2] All are called to holiness: "Be perfect, as your heavenly Father is perfect." [Mt 5:48] [915, 2545, 825]
In order to reach this perfection the faithful should use the strength dealt out to them by Christ's gift, so that... doing the will of the Father in everything, they may wholeheartedly devote themselves to the glory of God and to the service of their neighbor. Thus the holiness of the People of God will grow in fruitful abundance, as is clearly shown in the history of the Church through the lives of so many saints. [LG 40 § 2]
2014 Spiritual progress tends toward ever more intimate union with Christ. This union is called "mystical" because it participates in the mystery of Christ through the sacraments - "the holy mysteries" - and, in him, in the mystery of the Holy Trinity. God calls us all to this intimate union with him, even if the special graces or extraordinary signs of this mystical life are granted only to some for the sake of manifesting the gratuitous gift given to all. 
2015 The way of perfection passes by way of the Cross. There is no holiness without renunciation and spiritual battle. [Cf. 2 Tim 4] Spiritual progress entails the ascesis and mortification that gradually lead to living in the peace and joy of the Beatitudes: [407, 2725, 1438]
He who climbs never stops going from beginning to beginning, through beginnings that have no end. He never stops desiring what he already knows. [St. Gregory of Nyssa, Hom. in Cant. 8: PG 44, 941C]
2016 The children of our holy mother the Church rightly hope for the grace of final perseverance and the recompense of God their Father for the good works accomplished with his grace in communion with Jesus. [Cf. Council of Trent (1547): DS 1576] Keeping the same rule of life, believers share the "blessed hope" of those whom the divine mercy gathers into the "holy city, the new Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband." [Rev 21:2] [162, 1821, 1274]
2017 The grace of the Holy Spirit confers upon us the righteousness of God. Uniting us by faith and Baptism to the Passion and Resurrection of Christ, the Spirit makes us sharers in his life.
2018 Like conversion, justification has two aspects. Moved by grace, man turns toward God and away from sin, and so accepts forgiveness and righteousness from on high.
2019 Justification includes the remission of sins, sanctification, and the renewal of the inner man.
2020 Justification has been merited for us by the Passion of Christ. It is granted us through Baptism. It conforms us to the righteousness of God, who justifies us. It has for its goal the glory of God and of Christ, and the gift of eternal life. It is the most excellent work of God's mercy.
2021 Grace is the help God gives us to respond to our vocation of becoming his adopted sons. It introduces us into the intimacy of the Trinitarian life.
2022 The divine initiative in the work of grace precedes, prepares, and elicits the free response of man. Grace responds to the deepest yearnings of human freedom, calls freedom to cooperate with it, and perfects freedom.
2023 Sanctifying grace is the gratuitous gift of his life that God makes to us; it is infused by the Holy Spirit into the soul to heal it of sin and to sanctify it.
2024 Sanctifying grace makes us "pleasing to God." Charisms, special graces of the Holy Spirit, are oriented to sanctifying grace and are intended for the common good of the Church. God also acts through many actual graces, to be distinguished from habitual grace which is permanent in us.
2025 We can have merit in God's sight only because of God's free plan to associate man with the work of his grace. Merit is to be ascribed in the first place to the grace of God, and secondly to man's collaboration. Man's merit is due to God.
2026 The grace of the Holy Spirit can confer true merit on us, by virtue of our adoptive filiation, and in accordance with God's gratuitous justice. Charity is the principal source of merit in us before God.
2027 No one can merit the initial grace which is at the origin of conversion. Moved by the Holy Spirit, we can merit for ourselves and for others all the graces needed to attain eternal life, as well as necessary temporal goods.
2028 "All Christians... are called to the fullness of Christian life and to the perfection of charity" (LG 40 § 2). "Christian perfection has but one limit, that of having none" (St. Gregory of Nyssa, De vita Mos.: PG 44, 300D).
2029 "If any man would come after me, let him deny himself and take up his cross and follow me" (Mt 16:24).
THE CHURCH, MOTHER AND TEACHER
2030 It is in the Church, in communion with all the baptized, that the Christian fulfills his vocation. From the Church he receives the Word of God containing the teachings of "the law of Christ." From the Church he receives the grace of the sacraments that sustains him on the "way." From the Church he learns the example of holiness and recognizes its model and source in the all-holy Virgin Mary; he discerns it in the authentic witness of those who live it; he discovers it in the spiritual tradition and long history of the saints who have gone before him and whom the liturgy celebrates in the rhythms of the sanctoral cycle. [828, 1172]
2031 The moral life is spiritual worship. We "present [our] bodies as a living sacrifice, holy and acceptable to God," [Rom 12:1] within the Body of Christ that we form and in communion with the offering of his Eucharist. In the liturgy and the celebration of the sacraments, prayer and teaching are conjoined with the grace of Christ to enlighten and nourish Christian activity. As does the whole of the Christian life, the moral life finds its source and summit in the Eucharistic sacrifice. 
I. MORAL LIFE AND THE MAGISTERIUM OF THE CHURCH [85-87, 888-892]
2032 The Church, the "pillar and bulwark of the truth," "has received this solemn command of Christ from the apostles to announce the saving truth." [1 Tim 3:15; LG 17] "To the Church belongs the right always and everywhere to announce moral principles, including those pertaining to the social order, and to make judgments on any human affairs to the extent that they are required by the fundamental rights of the human person or the salvation of souls." [CIC, can. 747 § 2] [2246, 2420]
2033 The Magisterium of the Pastors of the Church in moral matters is ordinarily exercised in catechesis and preaching, with the help of the works of theologians and spiritual authors. Thus from generation to generation, under the aegis and vigilance of the pastors, the "deposit" of Christian moral teaching has been handed on, a deposit composed of a characteristic body of rules, commandments, and virtues proceeding from faith in Christ and animated by charity. Alongside the Creed and the Our Father, the basis for this catechesis has traditionally been the Decalogue which sets out the principles of moral life valid for all men. 
2034 The Roman Pontiff and the bishops are "authentic teachers, that is, teachers endowed with the authority of Christ, who preach the faith to the people entrusted to them, the faith to be believed and put into practice." [LG 25] The ordinary and universal Magisterium of the Pope and the bishops in communion with him teach the faithful the truth to believe, the charity to practice, the beatitude to hope for.
2035 The supreme degree of participation in the authority of Christ is ensured by the charism of infallibility. This infallibility extends as far as does the deposit of divine Revelation; it also extends to all those elements of doctrine, including morals, without which the saving truths of the faith cannot be preserved, explained, or observed. [Cf. LG 25; CDF, declaration, Mysterium Ecclesiae 3]
2036 The authority of the Magisterium extends also to the specific precepts of the natural law, because their observance, demanded by the Creator, is necessary for salvation. In recalling the prescriptions of the natural law, the Magisterium of the Church exercises an essential part of its prophetic office of proclaiming to men what they truly are and reminding them of what they should be before God. [Cf. DH 14] 
2037 The law of God entrusted to the Church is taught to the faithful as the way of life and truth. The faithful therefore have the right to be instructed in the divine saving precepts that purify judgment and, with grace, heal wounded human reason. [Cf. CIC, can. 213] They have the duty of observing the constitutions and decrees conveyed by the legitimate authority of the Church. Even if they concern disciplinary matters, these determinations call for docility in charity. 
2038 In the work of teaching and applying Christian morality, the Church needs the dedication of pastors, the knowledge of theologians, and the contribution of all Christians and men of good will. Faith and the practice of the Gospel provide each person with an experience of life "in Christ," who enlightens him and makes him able to evaluate the divine and human realities according to the Spirit of God. [Cf. 1 Cor 2:10-15] Thus the Holy Spirit can use the humblest to enlighten the learned and those in the highest positions. 
2039 Ministries should be exercised in a spirit of fraternal service and dedication to the Church, in the name of the Lord. [Cf. Rom 12:8, 11] At the same time the conscience of each person should avoid confining itself to individualistic considerations in its moral judgments of the person's own acts. As far as possible conscience should take account of the good of all, as expressed in the moral law, natural and revealed, and consequently in the law of the Church and in the authoritative teaching of the Magisterium on moral questions. Personal conscience and reason should not be set in opposition to the moral law or the Magisterium of the Church. 
2040 Thus a true filial spirit toward the Church can develop among Christians. It is the normal flowering of the baptismal grace which has begotten us in the womb of the Church and made us members of the Body of Christ. In her motherly care, the Church grants us the mercy of God which prevails over all our sins and is especially at work in the sacrament of reconciliation. With a mother's foresight, she also lavishes on us day after day in her liturgy the nourishment of the Word and Eucharist of the Lord. 
II. THE PRECEPTS OF THE CHURCH
2041 The precepts of the Church are set in the context of a moral life bound to and nourished by liturgical life. The obligatory character of these positive laws decreed by the pastoral authorities is meant to guarantee to the faithful the very necessary minimum in the spirit of prayer and moral effort, in the growth in love of God and neighbor:
2042 The first precept ("You shall attend Mass on Sundays and on holy days of obligation and rest from servile labour.") requires the faithful to sanctify the day commemorating the resurrection of the Lord as well as the principal liturgical feasts honoring the mysteries of the Lord, the Blessed Virgin Mary and the saints; in the first place, by participating in the Eucharistic celebration, in which the Christian community is gathered, and by resting from those works and activities which could impede such a sanctification of these days. [Cf. CIC, cann. 1246-1248; CCEO, can. 880 § 3, 881 §§ 1,2,4.] [1389, 2180]
The second precept ("You shall confess your sins at least once a year.") ensures preparation for the Eucharist by the reception of the sacrament of reconciliation, which continues Baptism's work of conversion and forgiveness. [Cf. CIC, can. 989; CCEO, can. 719] 
The third precept ("You shall receive the sacrament of the Eucharist at least during the Easter season.") guarantees as a minimum the reception of the Lord's Body and Blood in connection with the Paschal feasts, the origin and center of the Christian liturgy. [Cf. CIC, can. 920; CCEO, cann. 708; 881 § 3] 
2043 The fourth precept ("You shall observe the days of fasting and abstinence established by the Church") ensures the times of ascesis and penance which prepare us for the liturgical feasts and help us acquire mastery over our instincts and freedom of heart. [Cf. CIC, can. 1249-1251; CCEO, cann. 882] 
The fifth precept ("You shall help to provide for the needs of the Church") means that the faithful are obliged to assist with the material needs of the Church, each according to his own ability. [Cf. CIC, cann. 222; CEO, can. 25; Furthermore, episcopal conferences can establish other ecclesiastical precepts for their own territories (Cf. CIC, can. 455).] [1387, 1438]
III. MORAL LIFE AND MISSIONARY WITNESS
2044 The fidelity of the baptized is a primordial condition for the proclamation of the Gospel and for the Church's mission in the world. In order that the message of salvation can show the power of its truth and radiance before men, it must be authenticated by the witness of the life of Christians. "The witness of a Christian life and good works done in a supernatural spirit have great power to draw men to the faith and to God." [AA 6 § 2] [852, 905]
2045 Because they are members of the Body whose Head is Christ, [Cf. Eph 1:22] Christians contribute to building up the Church by the constancy of their convictions and their moral lives. The Church increases, grows, and develops through the holiness of her faithful, until "we all attain to the unity of the faith and of the knowledge of the Son of God, to mature manhood, to the measure of the stature of the fullness of Christ." [Eph 4:13; cf. LG 39] [753, 828]
2046 By living with the mind of Christ, Christians hasten the coming of the Reign of God, "a kingdom of justice, love, and peace." [Roman Missal, Preface of Christ the King] They do not, for all that, abandon their earthly tasks; faithful to their master, they fulfill them with uprightness, patience, and love. [671, 2819]
2047 The moral life is a spiritual worship. Christian activity finds its nourishment in the liturgy and the celebration of the sacraments.
2048 The precepts of the Church concern the moral and Christian life united with the liturgy and nourished by it.
2049 The Magisterium of the Pastors of the Church in moral matters is ordinarily exercised in catechesis and preaching, on the basis of the Decalogue which states the principles of moral life valid for every man.
2050 The Roman Pontiff and the bishops, as authentic teachers, preach to the People of God the faith which is to be believed and applied in moral life. It is also encumbent on them to pronounce on moral questions that fall within the natural law and reason.
2051 The infallibility of the Magisterium of the Pastors extends to all the elements of doctrine, including moral doctrine, without which the saving truths of the faith cannot be preserved, expounded, or observed.
THE TEN COMMANDMENTS
I am the LORD your God, who brought you out of the land of Egypt, out of the house of bondage.
You shall have no other gods before me. You shall not make for yourself a graven image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth; you shall not bow down to them or serve them; for I the LORD your God am a jealous God, visiting the iniquity of the fathers upon the children to the third and the fourth generation of those who hate me, but showing steadfast love to thousands of those who love me and keep my commandments.
You shall not take the name of the LORD your God in vain; for the LORD will not hold him guiltless who takes his name in vain.
Remember the sabbath day, to keep it holy. Six days you shall labor, and do all your work; but the seventh day is a sabbath to the LORD your God; in it you shall not do any work, you, or your son, or your daughter, your manservant or your maidservant or your cattle, or the sojourner who is within your gates; for in six days the LORD made heaven and earth, the sea, and all that is in them, and rested the seventh day; therefore the Lord blessed the sabbath day and hallowed it.
Honor your father and your mother, that your days may be long in the land which the LORD your God gives you.
You shall not kill.
You shall not commit adultery.
You shall not steal.
You shall not bear false witness against your neighbor.
You shall not covet your neighbor's house; you shall not covet your neighbor's wife, or his manservant or his maidservant or his ox, or his ass, or anything that is your neighbor's.
I am the LORD your God, who brought you out of the land of Egypt out of the house of bondage.
You shall have no other gods before me...
You shall not take the name of the LORD your God in vain; for the LORD will not hold him guiltless who takes his name in vain.
Observe the sabbath day, to keep it holy...
Honor your father and your mother...
You shall not kill.
Neither shall you commit adultery.
Neither shall you steal.
Neither shall you bear false witness against your neighbor.
Neither shall you covet your neighbor's wife.
You shall not desire... anything that is your neighbor's.
A Traditional Catechetical formula
1. I am the LORD your God: you shall not have strange Gods before me.
2. You shall not take the name of the LORD your God in vain.
3. Remember to keep holy the LORD'S Day.
4. Honor your father and your mother.
5. You shall not kill.
6. You shall not commit adultery.
7. You shall not steal.
8. You shall not bear false witness against your neighbor.
9. You shall not covet your neighbor's wife.
10. You shall not covet your neighbor's goods.