What does Proverbs 21:2 mean?

The Lord can control the hearts of anyone, even a king (Proverbs 21:1), because He knows the smallest details of our inner thoughts. A person may think his behavior is fine, but the ultimate Judge is God. No matter how good a person may think he is, the Lord looks upon the heart and sees whatever sin is there. Other Scriptures indicate our hearts are prone to self-deception about sin (Jeremiah 17:9). People may judge each other, assuming they can know with perfection who is good, but the Lord sees what we cannot see (1 Samuel 16:7).

Ultimately, all people have a level of sin in their inner being. The Bible notes that "none is righteous, no, not one" (Romans 3:10). The same passage also declares, "for all have sinned and fall short of the glory of God" (Romans 3:23). The Pharisee who stood in the temple and arrogantly compared himself to others, including someone who stood nearby, thought he was righteous because he performed religious acts. However, God knew his heart and did not justify him. He justified the person who acknowledged his sin and prayed, "God, be merciful to me, a sinner" (Luke 18:13).