Job and David understood sin. They were humble enough to bow themselves before God and acknowledge His sovereignty, His right to decide what is good and what is sin. They also understood that God loves them completely, and that they can put themselves in His hands.
Job 40. 3, 4: Then Job answered the LORD, and said, Behold, I am vile; what shall I answer thee? I will lay mine hand upon my mouth.
Psalm 51. 2, 3: Wash me thoroughly from mine iniquity, and cleanse me from my sin. For I acknowledge my transgressions: and my sin is ever before me.
This brings me to my knees.