In Roman Catholicism, mortal sin is a serious and willful transgression of God’s Law. It involves the full knowledge and intent of the will to commit the sin. If left unrepentant and not dealt with through penance, according to Catholicism, mortal sin can damn someone to eternal hell. Mortal sin is more serious than Venial Sin.

Examples of Mortal Sin would be murder, adultery, homosexuality, etc.

• “Mortal sin requires full knowledge and complete consent. It presupposes knowledge of the sinful character of the act, of its opposition to God’s law. It also implies a consent sufficiently deliberate to be a personal choice,” (Catechism of the Catholic Church, par. 1859).
• “Mortal sin is a radical possibility of human freedom, as is love itself. It results in the loss of charity and the privation of sanctifying grace, that is, of the state of grace,” (Catechism of the Catholic Church, par. 1861).