What does Psalm 139:16 mean?
This Scripture affirms that God knows everything about our lives, in advance, with His perfect omniscience. The Lord saw David's unborn state and planned the days David would live.No human being can predict accurately how long he or she will live. Proverbs 27:1 warns us not be presumptuous, "Do not boast about tomorrow," it warns, "for you do not know what a day may bring." James counseled: "Come now, you who say, 'Today or tomorrow we will go into such and such a town and spend a year there and trade and make a profit'—yet you do not know what tomorrow will bring" (James 4:13–14). How should we deal with the reality that we do not know how many days we will live? James said we should live each day doing the Lord's will and trusting that the results are ultimately up to Him (James 4:15).
Also, we should pray as Moses did, "So teach us to number our days that we may get a heart of wisdom" (Psalm 90:12).
Psalm 139:13–16 describes God's omnipotence: His attribute of being all-powerful. The psalmist, David, described God's omniscience in verses 1–6 and His omnipresence in verses 7–12. In this section, he links omnipotence to the way God created the writer in his mother's womb.
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.