What does Proverbs 5:21 mean?
If an adulterer thinks his sin is a secret, he deceives himself. Nothing is hidden from God's eyes (Hebrews 4:13). He sees all, and He knows all. One of the ways we justify sin to ourselves, often, is by pretending that no one will know. But God—whose knowledge matters more than that of any other person—can't be fooled or hidden from.This idea of God seeing and knowing all pervades Scripture. Genesis 6:5 reports that in the days just before the flood, "The LORD saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually." When Abraham expelled Hagar and Ishmael from his house, Hagar rested by a spring of water in the desert and received a visit from the angel of the Lord. After the visit, she called the name of the Lord, "You are a God of seeing" (Genesis 16:13). Amid his trials, Job said of God, "He knows the way that I take" (Job 23:10). Psalm 139:1–3 confesses "O LORD, you have searched me and known me! You know when I sit down and when I rise up; you discern my thoughts from afar. You search out my path and my lying down and are acquainted with all my ways."
The thought of the Lord's all-seeing eye brings comfort to those who walk uprightly, but it brings guilt and fear to those who pursue wickedness.