Q. 1. If one has a homosexual desire, is that a mortal sin?
A. 1. If of all, we have to consider if one can sin by desire. What would Jesus say on this matter? In the Gospel of Matthew, we read: "You have heard that it was said, 'You shall not commit adultery.' But I say to you that everyone who looks at a woman with lust has already commited adultery with her in his heart.' [Mt. 5:27-28]
Equally, it can be said, anyone who craves for a person of the same gender, who longs for such a person, who desires such a person, has already committed the sin of homosexuality in his heart.
It is not a sin to have a sinful thought, providing one is not intentionally attracting or entertaining such a thought. "Watch and pray, that ye enter not into temptation: the spirit indeed is willing, but the flesh is weak." [Mt. 26:41] Humans will always have sinful thoughts popping up in their minds; that is human nature, man being drawn to the woman and vice-versa. But such thoughts must end there. That is what separates the human from the animal. The human has a free will and self-control. The animal follows its instinct and goes after the opposite gender in order to breed.
So is a homosexual desire a sin? Yes, it is.
Q. 2. Is the homosexual desire a mortal sin?
A. 2. In the Holy Bible, we read, "Do you not know that wrongdoers will not inherit the Kingdom of God? Do not be deceived! Fornicators, idolaters, adulterers, male prostitutes, sodomites, thieves, the greedy, drunkards, revilers, robbers - none of these will inherit the Kingdom of God." [1 Cor. 6:9-10]
For a sin to be mortal, three conditions must exist at the same time.
1. It must be of a grave matter;
2. It must be committed with full knowledge that it is a mortal sin;
3. It must be committed with full consent. [Full consent means to do it "voluntarily."] (C.C.C. # 1857)
To be denied entry into the Kingdom of God, the sinner must:
1. Commit one or more sins of a grave matter;
2. Have full knowledge that the sin(s) is a mortal sin;
3. Voluntarily consent to commit the sin;
4. Reject the grace of God;
5. Reject the mercy of God by refusing to confess his sins through the Sacrament of Reconciliation.
The Catechism of the Catholic Church defines a mortal sin as follows:
"Mortal sin, by attacking the vital principle within us - that is, charity - necessitates a new initiative of God's mercy and a conversion of heart which is normally accomplished within the setting of the Sacrament of Confession." (C.C.C. # 1856)
"Mortal sin is a radical possibility of human freedom, as is love itself. It results in the loss of charity and the private of sanctifying grace, that is, of the state of grace. If it is not redeemed by repentance of God's forgiveness, it causes exclusion to make choices for ever, with no turning back. However, although we can judge that an act is in itself a grave offense, we must entrust judgment of persons to the justice and mercy of God." (C.C.C. # 1861)
"To choose deliberately - that is, both knowing it and willing it - something gravely contrary to the divine law and to the ultimate end of man is to commit a mortal sin. This destroys in us the charity without which eternal beatitude is impossible. Unrepented, it brings eternal death." (C.C.C. # 1874)