The Bible distinguishes several forms of sin. All are serious in the eyes of God, but they show themselves in different ways: through actions, omissions, thoughts or intentions.
1. Sins of commission
Galatians 5.19-21: The works of the flesh include sexual immorality, hatred, idolatry, and so on.
Exodus 20.13-17: The Ten Commandments forbid acts such as murder, theft and adultery.
Romans 1.29-31: Man left to himself commits acts of wickedness, pride and rebellion.
These are visible, deliberate sins, contrary to the divine law. They are intentional acts that transgress God's moral law.
2. Sins of omission
James 4.17: Failing to do good when one knows it is a sin.
Matthew 25.42-45: The refusal to help the needy is condemned.
Proverbs 24.11-12: Failing to intervene to save the innocent is a fault.
Sin can also be the absence of righteous or charitable action. Sin does not consist only in doing evil, but also in not doing good when one has the opportunity.
3. Sins of thought
Matthew 5.28: Lust in the heart is already adultery.
Mark 7.21-23: Evil thoughts come from the heart.
Proverbs 6.16-18: God hates evil thoughts and wicked schemes.
Sin begins in the intention, even without any outward act. God sees the hidden intention, not only the outward act.
4. Willful and unintentional sins
Leviticus 4.2: Sacrifices are prescribed for unintentional sins.
Luke 12.47-48: The one who knows and does not do it will be punished more severely.
Psalms 19.12: David asks forgiveness for the faults he does not know of.
God distinguishes sins according to the awareness of the guilty person, but all require cleansing. Unintentional sin shows that God's holiness demands reparation, even when man does not measure his fault.
Summary: The types of sin
Sin shows itself in different forms: through visible and deliberate acts that transgress the divine law, through omissions when the good is not done, through inner thoughts that God sees and judges, and even through unintentional faults that require cleansing. The holiness of God is such that every sin, conscious or not, demands reparation. Only the grace of the Messiah can cover all these forms of transgression.
Sin takes many forms, but the solution is one: forgiveness in Jesus Christ.