Your eyes saw my substance, being yet unformed. And in Your book they all were written, the days fashioned for me, when as yet there were none of them (Psalm 139.16).
Some believe this verse teaches that David’s days were all mapped out in advance. Some believe that it was his yet unformed embryonic members that were planned and known by God before the many, day-by-day stages of their development. Grammatically, it seems it could go either way. But I think the context seems to point toward the development of the embryo here. It is a reminder of God’s great care in planning our development within the womb. Woe to those who interfere!
One thing we know for certain is that this verse shouldn’t be used to create a sense of fatalism within us as we opt for the former interpretation. My times are in God’s hands. I am indestructible until I accomplish his will. I maintain this understanding of God’s power and sovereignty to take care of me throughout my life. But I also understand my responsibility as a steward before Him. I may cut my days short by living in sin, eating in an unhealthy manner, or taking foolish risks with my life. It is certain that each believer is God’s workmanship, created in Christ Jesus for good works, which God prepared beforehand that we should walk in them (Ephesians 2.10). It is also true that we might refuse to walk in these works God has prepared or even cut our lives short and never have the opportunity to walk in them. Both divine sovereignty and human responsibility must be maintained.