John Calvin Commentary Acts 26:9

"I verily thought with myself that I ought to do many things contrary to the name of Jesus of Nazareth." — Acts 26:9 (ASV)

And I truly. If Paul had not spoken more things than those which Luke has until now recited, his speech would not have held together well. From this we prove what was said before: that after he had spoken of the covenant of God, he then spoke of the grace and office of Christ, as the subject required.

He repeats the history of his conversion for this reason: not only that he may remove from himself all suspicion of instability, but also that he may testify that God had called him, and that he was even compelled by a commandment coming from heaven. For, since he was, contrary to his expectation, suddenly made a sheep from a wolf, such a violent change is of no small importance in gaining credibility for his doctrine.

Therefore, he emphasizes his fervor and vehement desire to punish the members of Christ, and also that stubbornness to which he was wholly given over. If he had been raised in the faith of Christ from his youth, or if he had been taught by some man, he would have embraced it willingly and without resistance; he himself would have been sure of his calling, but it would not have been so well known to others. But now, since, being inflamed with obstinate and immoderate fury, being moved by no external cause, nor persuaded by any human being, he changes his mind, it appears that he was tamed and subdued by the hand of God.

Therefore, this contrast is of great significance, in that he says that he was so puffed up with pride that he thought he would gain victory over Christ, by which he teaches that it was by no means through his own effort that he became a disciple of Christ. The name "Jesus of Nazareth" is used here to represent the entire profession of the gospel, which Paul sought to extinguish by making war ignorantly against God, as we can see.