mortal sin

A mortal sin (Latin: peccātum mortāle) is, in Christian theology, a gravely sinful act that leads to damnation if a person does not repent before death. It is also referred to as a deadly, grave, or serious sin. The concept is found in both Catholicism and Lutheranism. In Catholic theology, a mortal sin separates a person from God's saving grace. Three conditions must be met for a sin to be considered mortal: the act must involve "grave matter", be committed with "full knowledge", and be performed with "full and deliberate consent".

Examples of grave matter often relate to violations of the Ten Commandments. Common pastoral examples include getting drunk, engaging in unlawful sexual activity, stealing a substantial amount of property, or deliberately missing mass on Sunday or Holy Days of Obligation. The "sin against the Holy Spirit" and the "sins that cry to Heaven for vengeance" are also regarded as especially serious. According to Denis O'Callaghan, a Catholic priest, mortal sin can be understood not only as an action but as a state of separation from God. Bill Cosgrove, another priest, similarly notes that sin involves a person's goals and priorities, not only individual acts.