MAN'S RESPONSE TO GOD
142 By his Revelation, "the invisible God, from the fullness of his love, addresses men as his friends, and moves among them, in order to invite and receive them into his own company." [DV 2; cf. Col 1:15; I Tim 1:17; Ex 33:11; Jn 15:14-15; Bar 3:38 (Vulg.).] The adequate response to this invitation is faith. 
143 By faith, man completely submits his intellect and his will to God. [Cf. DV 5.] With his whole being man gives his assent to God the revealer. Sacred Scripture calls this human response to God, the author of revelation, "the obedience of faith". [Cf. Rom 1:5; 16:26.] 
THE OBEDIENCE OF FAITH
144 To obey (from the Latin ob-audire, to "hear or listen to") in faith is to submit freely to the word that has been heard, because its truth is guaranteed by God, who is Truth itself. Abraham is the model of such obedience offered us by Sacred Scripture. The Virgin Mary is its most perfect embodiment.
Abraham - "father of all who believe"
145 The Letter to the Hebrews, in its great eulogy of the faith of Israel's ancestors, lays special emphasis on Abraham's faith: "By faith, Abraham obeyed when he was called to go out to a place which he was to receive as an inheritance; and he went out, not knowing where he was to go." [Heb 11:8; cf. Gen 12:1-4.] By faith, he lived as a stranger and pilgrim in the promised land. [Cf. Gen 23:4.] By faith, Sarah was given to conceive the son of the promise. And by faith Abraham offered his only son in sacrifice. [Cf. Heb 11:17.] [59, 2570, 489]
146 Abraham thus fulfils the definition of faith in Hebrews 11:1: "Faith is the assurance of things hoped for, the conviction of things not seen": [Heb 11:1.] "Abraham believed God, and it was reckoned to him as righteousness." [Rom 4:3; cf. Gen 15:6.] Because he was "strong in his faith", Abraham became the "father of all who believe". [Rom 4:11, 18; 4:20; cf. Gen 15:5.] 
147 The Old Testament is rich in witnesses to this faith. The Letter to the Hebrews proclaims its eulogy of the exemplary faith of the ancestors who "received divine approval". [Heb 11:2, 39.] Yet "God had foreseen something better for us": the grace of believing in his Son Jesus, "the pioneer and perfecter of our faith". [Heb 11:40; 12:2.] 
Mary - "Blessed is she who believed"
148 The Virgin Mary most perfectly embodies the obedience of faith. By faith Mary welcomes the tidings and promise brought by the angel Gabriel, believing that "with God nothing will be impossible" and so giving her assent: "Behold I am the handmaid of the Lord; let it be [done] to me according to your word." [Lk 1:37-38; cf. Gen 18:14.] Elizabeth greeted her: "Blessed is she who believed that there would be a fulfilment of what was spoken to her from the Lord." [Lk 1:45.] It is for this faith that all generations have called Mary blessed. [Cf. Lk 1:48.] [494, 2617, 506]
149 Throughout her life and until her last ordeal [Cf. Lk 2:35.] when Jesus her son died on the cross, Mary's faith never wavered. She never ceased to believe in the fulfilment of God's word. And so the Church venerates in Mary the purest realization of faith. [969, 507, 829]
II. "I KNOW WHOM I HAVE BELIEVED"[2 Tim 1:12.]
To believe in God alone
150 Faith is first of all a personal adherence of man to God. At the same time, and inseparably, it is a free assent to the whole truth that God has revealed. As personal adherence to God and assent to his truth, Christian faith differs from our faith in any human person. It is right and just to entrust oneself wholly to God and to believe absolutely what he says. It would be futile and false to place such faith in a creature. [Cf. Jer 17:5-6; Pss 40:5; 146:3-4.] 
To believe in Jesus Christ, the Son of God
151 For a Christian, believing in God cannot be separated from believing in the One he sent, his "beloved Son", in whom the Father is "well pleased"; God tells us to listen to him. [Mk 1:11; cf. 9:7] The Lord himself said to his disciples: "Believe in God, believe also in me." [Jn 14:1.] We can believe in Jesus Christ because he is himself God, the Word made flesh: "No one has ever seen God; the only Son, who is in the bosom of the Father, he has made him known." [Jn 1:18.] Because he "has seen the Father", Jesus Christ is the only one who knows him and can reveal him. [Jn 6:46; cf. Mt 11:27.] 
To believe in the Holy Spirit
152 One cannot believe in Jesus Christ without sharing in his Spirit. It is the Holy Spirit who reveals to men who Jesus is. For "no one can say "Jesus is Lord", except by the Holy Spirit", [1 Cor 12:3.] who "searches everything, even the depths of God. . No one comprehends the thoughts of God, except the Spirit of God." [1 Cor 2:10-11.] Only God knows God completely: we believe in the Holy Spirit because he is God. [243, 683]
The Church never ceases to proclaim her faith in one only God: Father, Son and Holy Spirit. 
III. THE CHARACTERISTICS OF FAITH
Faith is a grace
153 When St. Peter confessed that Jesus is the Christ, the Son of the living God, Jesus declared to him that this revelation did not come "from flesh and blood", but from "my Father who is in heaven". [Mt 16:17; cf. Gal 1:15; Mt 11:25.] Faith is a gift of God, a supernatural virtue infused by him. "Before this faith can be exercised, man must have the grace of God to move and assist him; he must have the interior helps of the Holy Spirit, who moves the heart and converts it to God, who opens the eyes of the mind and 'makes it easy for all to accept and believe the truth.'" [DV 5; cf. DS 377; 3010.] [552, 1814, 1996, 2606]
Faith is a human act
154 Believing is possible only by grace and the interior helps of the Holy Spirit. But it is no less true that believing is an authentically human act. Trusting in God and cleaving to the truths he has revealed is contrary neither to human freedom nor to human reason. Even in human relations it is not contrary to our dignity to believe what other persons tell us about themselves and their intentions, or to trust their promises (for example, when a man and a woman marry) to share a communion of life with one another. If this is so, still less is it contrary to our dignity to "yield by faith the full submission of... intellect and will to God who reveals", [Dei Filius: 3: DS 3008.] and to share in an interior communion with him. [1749, 2126]
155 In faith, the human intellect and will co-operate with divine grace: "Believing is an act of the intellect assenting to the divine truth by command of the will moved by God through grace." [St. Thomas Aquinas, STh II-II, 2, 9; cf Dei Filius 3; DS 3010.] 
Faith and understanding
156 What moves us to believe is not the fact that revealed truths appear as true and intelligible in the light of our natural reason: we believe "because of the authority of God himself who reveals them, who can neither deceive nor be deceived". [Dei Filius: 3 DS 3008.] So "that the submission of our faith might nevertheless be in accordance with reason, God willed that external proofs of his Revelation should be joined to the internal helps of the Holy Spirit." [Dei Filius: 3 DS 3009.] Thus the miracles of Christ and the saints, prophecies, the Church's growth and holiness, and her fruitfulness and stability "are the most certain signs of divine Revelation, adapted to the intelligence of all"; they are "motives of credibility" (motiva credibilitatis) , which show that the assent of faith is "by no means a blind impulse of the mind". [Dei Filius: 3: DS 3008-3010; Cf. Mk 16 20; Heb 2:4.] [1063, 2465, 548, 812]
157 Faith is certain. It is more certain than all human knowledge because it is founded on the very word of God who cannot lie. To be sure, revealed truths can seem obscure to human reason and experience, but "the certainty that the divine light gives is greater than that which the light of natural reason gives." [St. Thomas Aquinas, STh II-II 171, 5, obj. 3.] "Ten thousand difficulties do not make one doubt." [John Henry Cardinal Newman, Apologia pro vita sua (London Longman, 1878) 239.] 
158 "Faith seeks understanding": [St. Anselm, Prosl. prooem. PL 153 225A.] it is intrinsic to faith that a believer desires to know better the One in whom he has put his faith, and to understand better what He has revealed; a more penetrating knowledge will in turn call forth a greater faith, increasingly set afire by love. The grace of faith opens "the eyes of your hearts" [Eph 1:18.] to a lively understanding of the contents of Revelation: that is, of the totality of God's plan and the mysteries of faith, of their connection with each other and with Christ, the centre of the revealed mystery. "The same Holy Spirit constantly perfects faith by his gifts, so that Revelation may be more and more profoundly understood." [DV 5.] In the words of St. Augustine, "I believe, in order to understand; and I understand, the better to believe." [St. Augustine, Sermo 43, 7, 9: PL 38, 257-258.] [2705, 1827, 90, 2518]
159 Faith and science: "Though faith is above reason, there can never be any real discrepancy between faith and reason. Since the same God who reveals mysteries and infuses faith has bestowed the light of reason on the human mind, God cannot deny himself, nor can truth ever contradict truth." [Dei Filius 4: DS 3017.] "Consequently, methodical research in all branches of knowledge, provided it is carried out in a truly scientific manner and does not override moral laws, can never conflict with the faith, because the things of the world and the things of faith derive from the same God. The humble and persevering investigator of the secrets of nature is being led, as it were, by the hand of God in spite of himself, for it is God, the conserver of all things, who made them what they are." [GS 36 § 1.] [283, 2293]
The freedom of faith
160 To be human, "man's response to God by faith must be free, and... therefore nobody is to be forced to embrace the faith against his will. The act of faith is of its very nature a free act." [DH 10; cf. CIC, can. 748 § 2.] "God calls men to serve him in spirit and in truth. Consequently they are bound to him in conscience, but not coerced... This fact received its fullest manifestation in Christ Jesus." [DH 11.] Indeed, Christ invited people to faith and conversion, but never coerced them. "For he bore witness to the truth but refused to use force to impose it on those who spoke against it. His kingdom... grows by the love with which Christ, lifted up on the cross, draws men to himself." [DH 11; cf. Jn 18:37; 12:32.] [1738, 2106, 616]
The necessity of faith
161 Believing in Jesus Christ and in the One who sent him for our salvation is necessary for obtaining that salvation. [Cf. Mk 16:16; Jn 3:36; 6:40 et al.] "Since "without faith it is impossible to please [God]" and to attain to the fellowship of his sons, therefore without faith no one has ever attained justification, nor will anyone obtain eternal life 'But he who endures to the end.'" [Dei Filius 3: DS 3012; cf. Mt 10:22; 24: 13 and Heb 11:6; Council of Trent: DS 1532.] [432, 1257, 846]
Perseverance in faith
162 Faith is an entirely free gift that God makes to man. We can lose this priceless gift, as St. Paul indicated to St. Timothy: "Wage the good warfare, holding faith and a good conscience. By rejecting conscience, certain persons have made shipwreck of their faith." [1 Tim 1:18-19.] To live, grow and persevere in the faith until the end we must nourish it with the word of God; we must beg the Lord to increase our faith; [Cf. Mk 9:24; Lk 17:5; 22:32] it must be "working through charity," abounding in hope, and rooted in the faith of the Church. [Gal 5:6; Rom 15:13; cf. Jas 2:14-26.] [2089, 1037, 2016, 2573, 2849]
Faith - the beginning of eternal life
163 Faith makes us taste in advance the light of the beatific vision, the goal of our journey here below. Then we shall see God "face to face", "as he is". [1 Cor 13:12; 1 Jn 3:2.] So faith is already the beginning of eternal life: 
When we contemplate the blessings of faith even now, as if gazing at a reflection in a mirror, it is as if we already possessed the wonderful things which our faith assures us we shall one day enjoy. [St. Basil De Spiritu Sancto 15, 36: PG 32, 132; cf. St. Thomas Aquinas, STh II-II, 4, 1.]
164 Now, however, "we walk by faith, not by sight"; [2 Cor 5:7.] we perceive God as "in a mirror, dimly" and only "in part". [l Cor 13:12.] Even though enlightened by him in whom it believes, faith is often lived in darkness and can be put to the test. The world we live in often seems very far from the one promised us by faith. Our experiences of evil and suffering, injustice and death, seem to contradict the Good News; they can shake our faith and become a temptation against it. [2846, 309, 1502, 1006]
165 It is then we must turn to the witnesses of faith: to Abraham, who "in hope... believed against hope"; [Rom 4:18.] to the Virgin Mary, who, in "her pilgrimage of faith", walked into the "night of faith" [LG 58; John Paul II, RMat 18.] in sharing the darkness of her son's suffering and death; and to so many others: "Therefore, since we are surrounded by so great a cloud of witnesses, let us also lay aside every weight, and sin which clings so closely, and let us run with perseverance the race that is set before us, looking to Jesus the pioneer and perfecter of our faith." [Heb 12:1-2. Article 2] 
166 Faith is a personal act - the free response of the human person to the initiative of God who reveals himself. But faith is not an isolated act. No one can believe alone, just as no one can live alone. You have not given yourself faith as you have not given yourself life. The believer has received faith from others and should hand it on to others. Our love for Jesus and for our neighbour impels us to speak to others about our faith. Each believer is thus a link in the great chain of believers. I cannot believe without being carried by the faith of others, and by my faith I help support others in the faith. 
167 "I believe" (Apostles' Creed) is the faith of the Church professed personally by each believer, principally during Baptism. "We believe" (Niceno-Constantinopolitan Creed) is the faith of the Church confessed by the bishops assembled in council or more generally by the liturgical assembly of believers. "I believe" is also the Church, our mother, responding to God by faith as she teaches us to say both "I believe" and "We believe". [1124, 2040]
I. "LORD, LOOK UPON THE FAITH OF YOUR CHURCH"
168 It is the Church that believes first, and so bears, nourishes and sustains my faith. Everywhere, it is the Church that first confesses the Lord: "Throughout the world the holy Church acclaims you", as we sing in the hymn Te Deum; with her and in her, we are won over and brought to confess: "I believe", "We believe". It is through the Church that we receive faith and new life in Christ by Baptism. In the Rituale Romanum, the minister of Baptism asks the catechumen: "What do you ask of God's Church?" And the answer is: "Faith." "What does faith offer you?" "Eternal life." [Roman Ritual, Rite of Baptism of Adults.] 
169 Salvation comes from God alone; but because we receive the life of faith through the Church, she is our mother: "We believe the Church as the mother of our new birth, and not in the Church as if she were the author of our salvation." [Faustus of Riez, De Spiritu Sancto 1, 2: PL 62, II.] Because she is our mother, she is also our teacher in the faith. [750, 2030]
II. THE LANGUAGE OF FAITH
170 We do not believe in formulae, but in those realities they express, which faith allows us to touch. "The believer's act [of faith] does not terminate in the propositions, but in the realities [which they express]." [St. Thomas Aquinas, STh II-II, 1,2, ad 2.] All the same, we do approach these realities with the help of formulations of the faith which permit us to express the faith and to hand it on, to celebrate it in community, to assimilate and live on it more and more. 
171 The Church, "the pillar and bulwark of the truth", faithfully guards "the faith which was once for all delivered to the saints". She guards the memory of Christ's words; it is she who from generation to generation hands on the apostles' confession of faith. [1 Tim 3:15; Jude 3.] As a mother who teaches her children to speak and so to understand and communicate, the Church our Mother teaches us the language of faith in order to introduce us to the understanding and the life of faith. [78, 857, 84, 185]
III. ONLY ONE FAITH
172 Through the centuries, in so many languages, cultures, peoples and nations, the Church has constantly confessed this one faith, received from the one Lord, transmitted by one Baptism, and grounded in the conviction that all people have only one God and Father. [Cf. Eph 4:4-6.] St. Irenaeus of Lyons, a witness of this faith, declared: 
173 "Indeed, the Church, though scattered throughout the whole world, even to the ends of the earth, having received the faith from the apostles and their disciples... guards [this preaching and faith] with care, as dwelling in but a single house, and similarly believes as if having but one soul and a single heart, and preaches, teaches and hands on this faith with a unanimous voice, as if possessing only one mouth." [St. Irenaeus, Adv. haeres. I, 10, 1-2: PG 7/1, 549-552.] 
174 "For though languages differ throughout the world, the content of the Tradition is one and the same. The Churches established in Germany have no other faith or Tradition, nor do those of the Iberians, nor those of the Celts, nor those of the East, of Egypt, of Libya, nor those established at the centre of the world..." [St. Irenaeus, Adv. haeres. I, 10, 1-2: PG 7/1, 552-553.] The Church's message "is true and solid, in which one and the same way of salvation appears throughout the whole world." [St. Irenaeus, Adv. haeres. 5, 20, I: PG 7/2, 1177.] 
175 "We guard with care the faith that we have received from the Church, for without ceasing, under the action of God's Spirit, this deposit of great price, as if in an excellent vessel, is constantly being renewed and causes the very vessel that contains it to be renewed." [St. Irenaeus, Adv. haeres. 3, 24, I: PG 7/1, 966.]
176 Faith is a personal adherence of the whole man to God who reveals himself. It involves an assent of the intellect and will to the self-revelation God has made through his deeds and words.
177 "To believe" has thus a twofold reference: to the person, and to the truth: to the truth, by trust in the person who bears witness to it.
178 We must believe in no one but God: the Father, the Son and the Holy Spirit.
179 Faith is a supernatural gift from God. In order to believe, man needs the interior helps of the Holy Spirit.
180 "Believing" is a human act, conscious and free, corresponding to the dignity of the human person.
181 "Believing" is an ecclesial act. The Church's faith precedes, engenders, supports and nourishes our faith. The Church is the mother of all believers. "No one can have God as Father who does not have the Church as Mother" (St. Cyprian, De unit. 6: PL 4, 519).
182 We believe all "that which is contained in the word of God, written or handed down, and which the Church proposes for belief as divinely revealed" (Paul VI, CPG § 20).
183 Faith is necessary for salvation. The Lord himself affirms: "He who believes and is baptized will be saved; but he who does not believe will be condemned" (Mk 16:16).
184 "Faith is a foretaste of the knowledge that will make us blessed in the life to come" (St. Thomas Aquinas. Comp. theol. 1, 2).
The Apostles' Creed
I believe in God the Father Almighty,
Creator of Heaven and earth;
I believe in Jesus Christ,
His only Son, our Lord,
He was conceived by the Holy Spirit
and born of the Virgin Mary. He suffered under Pontius Pilate,
was crucified, died, and was buried.
He descended to the dead.
On the third day He rose again.
He ascended into Heaven
and is seated at the right hand of the Father.
He will come again to judge the living and the dead.
I believe in the Holy Spirit,
the Holy Catholic Church,
the communion of Saints,
the forgiveness of sins,
the resurrection of the body,
and the life everlasting.
The Nicene Creed
We believe in God, the Father, the Almighty,
maker of heaven and earth,
and all that is seen and unseen.
We believe in one Lord, Jesus Christ,
the only Son of God, eternally begotten of the Father,
God from God, Light from Light,
true God from true God,
begotten, not made, one in Being with the Father.
Through him all things were made.
For us men and for our salvation
he came down from heaven:
by the power of the Holy Spirit
he was born of the Virgin Mary,
and became man.
For our sake he was crucified under Pontius Pilate;
he suffered, died, and was buried.
On the third day he rose again
in fulfilment of the Scriptures;
he ascended into heaven
and is seated at the right hand of the Father.
He will come again in glory
to judge the living and the dead,
and His kingdom will have no end.
We believe in the Holy Spirit,
the Lord, the giver of life,
who proceeds from the Father and the Son.
With the Father and the Son
he is worshipped and glorified.
He has spoken through the Prophets.
We believe in one holy catholic and apostolic Church.
We acknowledge one baptism for the forgiveness of sins.
We look for the resurrection of the dead,
and the life of the world to come.