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).