All sin is an offense against God and a rejection of his perfect love and justice. Yet, Jesus makes a distinction between two types of sins. We call the most serious and grave sins, mortal sins. Mortal sins destroy the grace of God in the heart of the sinner. By their very grave nature, a mortal sin cuts our relationship off from God and turns man away from his creator.
St. Paul’s letter to the Hebrews tell us that "if we sin willfully after having the knowledge of the truth, there is now left no sacrifice for sins" (Hebrews 10:26). The second type of sin, venial sin, that of less grave matter, does not cut us off from Christ. However, venial sin does weaken grace in the soul and damages our relationship with God. A person who frequently indulges in venial sin is very likely to collapse into mortal sin if they persist in their evil ways.