This is a Hebrew expression, meaning to sanctify, ordain, prepare. Paul is saying, "When I was not yet born God ordained me to be an apostle, and in due time confirmed my apostleship before the world. Every gift, be it small or great, spiritual or temporal, and every good thing I should ever do, God has ordained while I was yet in my mother's womb where I could neither think nor perform any good thing. After I was born God supported me. Heaping mercy upon mercy, He freely forgave my sins, replenishing me with His grace to enable me to learn what great things are ours in Christ. To crown it all, He called me to preach the Gospel to others."
VERSE 15. And called me by his grace.
"Did God call me on account of my holy life? Or on account of my pharisaical religion? Or on account of my prayers, fastings, and works? Never. Well, then, it is certain God did not call me on account of my blasphemies, persecutions, oppressions. What prompted Him to call me? His grace alone."
VERSE 16. To reveal his Son to me.
We now hear what kind of doctrine was committed to Paul: The doctrine of the Gospel, the doctrine of the revelation of the Son of God. This doctrine differs greatly from the Law. The Law terrorizes the conscience. The Law reveals the wrath and judgment of God. The Gospel does not threaten. The Gospel announces that Christ is come to forgive the sins of the world. The Gospel conveys to us the inestimable treasures of God.
VERSE 16. That I might preach him among the heathen.
"It pleased God," says the Apostle, "to reveal himself in me. Why? For a twofold purpose. That I personally should believe in the Son of God, and that I should reveal Him to the Gentiles."
Paul does not mention the Jews, for the simple reason that he was the called and acknowledged apostle of the Gentiles, although he preached Christ also to the Jews.
We can hear the Apostle saying to himself: "I will not burden the Gentiles with the Law, because I am their apostle and not their lawgiver. Not once did you Galatians hear me speak of the righteousness of the Law or of works. My job was to bring you the Gospel. Therefore you ought to listen to no teachers of the Law, but the Gospel: not Moses, but the Son of God; not the righteousness of works, but the righteousness of faith must be proclaimed to the Gentiles. That is the right kind of preaching for Gentiles."
VERSE 16. Immediately I conferred not with flesh and blood.