John Calvin Commentary Acts 9:29

"preaching boldly in the name of the Lord: and he spake and disputed against the Grecian Jews; but they were seeking to kill him." — Acts 9:29 (ASV)

He disputed with the Grecians. Erasmus notes well in this place that those here called Grecians are not those who were of Greek descent, but rather those Jews who were scattered throughout various parts of the world. These men were accustomed to come together to Jerusalem to worship. And it is thought that Paul disputed with strangers and foreigners, rather than with those who lived in Jerusalem, because this latter group would never have tolerated him, nor would it have been wise for him to appear before them. Therefore, excluded by those who knew him previously, he tested whether there was any hope of doing good among men he did not know. In this way, he most bravely performed whatever concerned the duty of a valiant soldier.

They would have slain him. Behold, again, fury instead of zeal; and it must be that hypocrisy and superstition will be cruel and fierce.

The godly must be incensed with a holy wrath when they see the pure truth of God corrupted by false and wicked opinions; yet they must moderate their zeal in such a way that, first, they decide nothing until they have thoroughly weighed the cause; second, they attempt to bring back to the way those who wander from it; and lastly, if they see that such people's stubbornness is beyond hope, they themselves do not take the sword in hand, because they must know that they have no authority granted to them by the Lord to punish or take revenge.

But hypocrites are always ready to shed blood before they know the matter, so that superstition is bloody through blind and reckless fury. But Paul, who recently went about to harass the godly, can now remain nowhere. And yet this condition was far better for him than if he had reigned in peace and quiet, driving the godly everywhere out of their places.