What does Psalm 139:1 mean?

David recalls that the Lord has searched him and known him. The word "searched," relates to digging deep into a mine (Job 28:3) or exploring a country. The same Hebrew root word is used of the Danites exploring a territory to claim as their own (Judges 18:2). David perceives that God has dug deeply into his heart, where He uncovered everything there.

Certainly, the Lord knows the condition of the human heart. His diagnosis is accurate. Jeremiah states "the heart is deceitful above all things, and desperately sick" (Jeremiah 17:9). He also describes the Lord as searching the heart and testing the mind (Jeremiah 17:10).

Sin entered the heart when Adam and Eve sinned, and it reached a fever pitch in the days before the flood, when "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" (Genesis 6:5). At one point in his life, David tried to hide the sin of adultery that he had committed with Bathsheba, but the Lord saw David's heart and exposed his sin (2 Samuel 11—12).