What does Galatians 1:15 mean?
In order to show his Galatian readers that what he taught them about Christ came directly from Christ, Paul is reminding them of his own story. He has described his years in Judaism, when he was a Pharisee. He was so opposed to Jesus of Nazareth that he arrested, imprisoned, and approved of the killing of Christians. He was so zealous for the traditions that he advance beyond his peers in Jewish leadership.Then everything changed. Paul's story is that God appeared to him and turned him around (Acts 9:1–22). Looking back, Paul says he now understands that God set him apart for this role of apostle before he was even born. In other words, Paul didn't simply rethink his life and change course. God intervened to put Paul in the role God had destined him to fill.
Secondly, Paul writes that God called him by His grace. Paul understood that just as nobody "earns" status before God, he had not "earned" the role of apostle. Paul only represented Christ to the Galatians, and to everyone else, by the grace of God. God did this to him; he did not choose it. He simply received it.