With this phrase, Paul is claiming that his call to apostleship was one which God had determined from his time in his mother’s womb. Essentially, he considers himself to be a prophet of God in the same category as Isaiah (Isaiah 49:1) and Jeremiah (Jeremiah 1:5). Paul did not volunteer to be an apostle and God did not wait for him to first prove himself.1 No, he was summoned by God in a compelling way,2 and his ministry would be a continuation of the work of the Servant of the LORD.3
15 But when he who had set me apart before I was born, and who called me by his grace,