Q. What is a mortal sin?
A. The Catechism of the Catholic Church defines a mortal sin as follows:
"Mortal sin destroys charity in the heart of man by a grave violation of God's law; it turns man away from God, who is his ultimate end and his beatitude, by preferring an inferior good to him." (C.C.C. # 1855)
"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)
Q. What is a venial sin?
A. The Catechism of the Catholic Church defines a venial sin as follows:
"Venial sin allows charity to subsist, even though it offends and wounds it." (To "subsist" means to "exist.") (C.C.C. # 1855)
"Venial sin constitutes a moral disorder that is reparable by charity, which it allows to subsist in us." (C.C.C. # 1875)
"One commits venial sin when, in a less serious matter, he does not observe the standard prescribed by the moral law,or when he disobeys the moral law in a grave matter, but without full knowledge or without complete consent." (C.C.C. #. 1862)
"Venial sin weakens charity; it manifests a disordered affection for created goods; it impedes the soul's progress in the exercise of the virtues and the practice of the moral good; it merits temporal punishment. Deliberate and unrepented venial sin disposes us little by little to commit mortal sin. However venial sin does not set us in direct opposition to the will and friendship of God; it does not break the covenant with God. With God's grace it is humanly reparable. 'Venial sin does not deprive the sinner of sanctifying grace, friendship with God, charity, and consequently eternal happiness.'" (C.C.C. # 1863)
Q. What is the difference between a mortal sin and a venial sin?
A. 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)
Grave matter is specified by the Ten Commandments, corresponding to the answer of Jesus to the rich young man: 'Do not kill, Do not commit adultery, Do not steal, Do not bear false witness, Do not defraud, Honor your father and mother.' The gravity of sins is more or less great: murder is graver than theft. One must also take into account who is wronged: violence against parents is in itself graver than violence against a stranger." (C.C.C. # 1858)
"Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God's laws. It also implies a consent sufficiently deliberate to be a personal choice. Feigned ignorance and hardness of heart do not diminish, but rather increase, the voluntary character of a sin." (C.C.C. # 1859)
"When the will sets itself upon something that is of its nature incompatible with the charity that orients man toward his ultimate end, then the sin is mortal by its very object... whether it contradicts the love of God, such as blasphemy or perjury, or the love of neighbour, such as homicide or adultery... But when the sinner's will is set upon something that of its nature involves a disorder, but is not opposed to the love of God and neighbour, such as thoughtless chatter or immoderate laughter and the like, such sins are venial." (C.C.C. # 1856)