John Calvin Commentary Acts 21:32

"And forthwith he took soldiers and centurions, and ran down upon them: and they, when they saw the chief captain and the soldiers, left off beating Paul." — Acts 21:32 (ASV)

And when they saw the chief captain. Those whose fury neither the majesty of God, nor even the reverence of the temple, could at all restrain, begin to relent when they see a profane man. This shows that they were set on fire rather with barbarous cruelty than with zeal.

Now, while the chief captain binds Paul with chains, he thereby sufficiently shows that he did not come to relieve him. The unbelievers would attribute this to fortune, but the Spirit has depicted for us the providence of God (as in a picture) reigning amidst the confused uproars of men.

And though it is very hard that this holy minister of God is so shamefully handled, yet the fairness of the chief captain is to be commended if he is compared with the Jews. He binds him with chains, as if he were some evildoer or wicked person; yet he deigns to hear him when he is bound, whom they beat unmercifully. Nor does he resolve to treat him harshly before he knew his cause.

Indeed, this was the best way to mitigate their cruelty, because they thought (and hoped) that Paul would be punished immediately.