The Bible simply does not teach that God predetermines our lives, especially in the sense of ultimate salvation. Some hold to this idea, which is called predestination. But from the beginning God has always given intelligent beings the faculty of choice. This includes the angels, Adam and Eve, the children of Israel and all people down through history.
Notice that Psalm 139 concludes with a prayer for deliverance from sin and asks God's guidance in learning His everlasting ways. Why would David ask that if he knew his salvation were assured no matter what? This request shows that he clearly didn't see himself as being guaranteed salvation. He knew that he, like all of us, needed God's direction to find the right path.
Earlier God had said of King Saul, "I greatly regret that I have set up Saul as king, for he has turned back from following Me, and has not performed My commandments" (1 Samuel 15:11). If God had predetermined the outcome of Saul's life, He wouldn't have chosen Him to be Israel's first king. A person who once had been humble (verse 17) had turned away from God and chosen the wrong path of life.
Jesus Christ taught the same thing: Individuals are free to choose. Jesus concludes the Sermon on the Mount with several examples that call for defining action on our part (see Matthew 7:13-28). He presents us with two mutually exclusive paths—one broad and easy, the other narrow and difficult.
We must find the right path that leads to salvation—discerning between two kinds of teachers, true ones and false ones. His true servants must hear His words and then do them to obtain salvation. This is also the message of the book of James. Read James 2:8-12.
Of course, it is implicit that we all must be saved by grace through the sacrifice of Christ, but God's forgiveness should always lead to a life of obedience. (For further understanding please request our free booklets The Road to Eternal Life and You Can Have Living Faith.)
No doubt God knows far more about us than we can imagine (1 Corinthians 13:12). But the teaching of the Bible is that individuals have freedom of choice and that we will be judged "according to our works" (Deuteronomy 30:19-20; Ecclesiastes 12:13-14; Acts 17:30-31; Revelation 20:13).
What does Psalm 139:13-16, then, mean? The most recent translation of the Old Testament by the Jewish Publication Society is the Tanakh. It translates this particular passage: "My frame is not concealed from You when I was shaped in a hidden place, knit together in the recesses of the earth. Your eyes saw my unformed limbs; they were all recorded in Your book; in due time they were formed, to the very last one of them."
The intent of this passage is to convey God's sovereignty over our lives beginning at conception, not to teach predestination. Our Creator is concerned that we fulfill our great purpose in life—to obtain everlasting life in the Kingdom of God—but we must willingly accept His salvation and practice His way of life. He wants us to choose rightly, but the choice is still ours. To understand more, please request our free booklet What Is Your Destiny?