Knowledge of Sin Comes Through the Law

Yes, people sinned even before the law was given. But it was not counted as sin because there was not yet any law to break. (Romans 5:13 NLT)

But I tell you that anyone who is angry with his brother will be subject to judgment. Again, anyone who says to his brother, 'Raca,' will be subject to the Sanhedrin. But anyone who says, 'You fool!' will be subject to the fire of hell. (Matthew 5:22 BSB)

But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart. (Matthew 5:28 NIV)

The law does not account for every sin.

For example, if a person has a very bad temper and gets angry easily, he does not break any law, unless he is so angry that he kills somebody.

A person who looks at a woman's cleavage (like what some famous person did recently and was caught in a video) has already committed adultery, but he does not break any law.

For by works of the law no human being will be justified in his sight, since through the law comes knowledge of sin. (Romans 3:20 ESV)