What does Psalm 139:2 mean?
David acknowledges in this verse that the Lord's knowledge is thorough and perfect. This is poetically summarized by saying God knows when David sits down and gets up. He even knows David's thoughts. He knows David's every motion and discerns everything about his thoughts. He discerns their moral quality and what motivates them.Hebrews 4:13 tells us, "No creature is hidden from his sight, but all are naked and exposed to the eyes of him to whom we must give account." When Jesus called Nathanael to be His disciple, He told him, "Before Philip called you, when you were under the fig tree, I saw you" (John 1:48). Nathanael was so amazed at Jesus' knowledge that he declared, "Rabbi, you are the Son of God! You are the King of Israel!" (John 1:49). John 2:24–25 says about Jesus, "he knew all people and needed no one to bear witness about man, for he himself knew what was in man."
Psalm 139:1–6 extols God's infinite knowledge. David views God as knowing all about him: when he sits down and gets up, his thoughts and conduct, and even the words that are in his mind before he expresses them. He states that God's knowledge is far beyond his comprehension. This section of the psalm precedes the section that focuses on God's omnipresence—his presence everywhere.
In this psalm David marvels at God's amazing characteristics. God knows everything about him: where he goes, all David's thoughts and everything about his conduct. The Lord knows what David will say even before David says it. There is no place David can go that God isn't already present. David marvels at God's creative work in the womb. He is thankful for God's innumerable thoughts for him and for God's presence day and night. Finally, David's thoughts turn to the wicked. He considers them God's enemies and his, and longs for God to slay them. David is disgusted by evil people because they rail against God and take His name in vain. He asks God to search his heart to see if any sin is there, and he asks God to lead him in the way everlasting.