Mortal sins are sins of serious or grave matter. “Mortal” means death; they are sins that cause death to the soul. Mortal sins completely sever one’s relationship with God and the sacrament of Penance and Reconciliation (commonly called Confession) is necessary to restore this relationship. Venial sins are less serious sins.
Scriptures tells us that there are sins that are deadly and sins that are not deadly in 1 John 5:16-17.
“If anyone sees his brother sinning, if the sin is not deadly, he should pray to God and he will give him life. This is only for those whose sin is not deadly. There is such a thing as deadly sin, about which I do not say that you should pray. All wrongdoing is sin, but there is sin that is not deadly.”
Conditions for Mortal Sins
Three conditions must be met to classify a sin as a mortal sin. All three of these conditions must be met otherwise the sin is considered a venial sin.
- Grave matter.
- Sufficiently full knowledge.
- Full consent or freedom.
Grave matter means that the sin must be of substantial significance. The Church uses Mark 10:19 as its guideline for what defines grave matter. “You shall not kill; you shall not commit adultery; you shall not steal; you shall not bear false witness; you shall not defraud; honor your father and your mother.” The Catechism of the Catholic Church instructs that “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.” (Paragraph 1858)
Sufficiently full knowledge means that one must fully know that the sin they are committing is serious and have the intention of breaking the relationship with God. Pretending not to know that the sin is wrong or having a hardness of heart actually magnify that the sin was a personal choice.
Full consent or freedom means that the person must fully and willingly commit the sin. If the person is being coerced to commit the act then it is not a mortal sin. It must be a choice made completely of one’s own free will, a conscious choice. This kind of choice is available to us through God’s gift of free will. God’s desire is for us to love him and making a conscious choice to commit mortal sins is the opposite of loving God.
Mortal sin deprives the soul of sanctifying grace. It kills one’s receptivity to that grace hence the reason it is important to go to confession to cleanse the soul of mortal sins.
The Unforgiveable Sin
The only sin that cannot be forgiven is blasphemy against the Holy Spirit (Mk 3:29; cf. Mt 12:31; Lk 12:10). Blasphemy against the Holy Spirit is the final and obdurate rejection of God’s forgiveness itself, stubbornly refusing forever to accept God’s outpouring of forgiveness.