What is the difference between mortal and venial sins?

The distinction between mortal and venial sins comes from Catholic theology, not from the pages of Scripture directly. Understanding where it comes from, what it claims, and how it compares to what the Bible actually teaches is important for any serious student of Scripture.

Catholic teaching distinguishes: mortal sins are grave offences committed with full knowledge and deliberate consent that break a person's relationship with God and, if unrepented, lead to eternal death. Venial sins are less serious offences that weaken but do not destroy the person's relationship with God. The basis is partly 1 John 5:16-17, which distinguishes between "sin that leads to death" and "sin that does not lead to death."

What does 1 John 5:16-17 actually mean? The most likely interpretation is that "sin leading to death" refers to apostasy — the final, definitive rejection of Christ — rather than a category of individual actions. This reading fits John's broader concern in his letters about those who had left the community and denied that Jesus is the Christ.

The broader biblical picture does not support a two-tier system of sin. James 2:10: "Whoever keeps the whole law but fails in one point has become guilty of all of it." In God's sight, the standard is perfect obedience — any deviation falls short. Romans 3:23 makes no distinctions: "All have sinned and fall short of the glory of God." There is no passage that divides sins into categories that either do or do not break your relationship with God.

What the Bible does recognise is that sins vary in their seriousness and consequences. Proverbs 6:16-19 lists things God especially hates. Jesus said Pilate's sin was less than the sin of those who handed Him over (John 19:11). Some sins bring greater earthly consequences. But the remedy for all sin is the same: repentance and faith in Christ, not degrees of penance.

The danger of the mortal/venial distinction is that it can produce either false security ("this is only venial") or unnecessary despair ("I have committed a mortal sin and must somehow restore myself"). The New Testament offers a simpler, more radical solution: confess, repent, and trust the blood of Jesus Christ which cleanses from all sin (1 John 1:7).