John Calvin Commentary Acts 21:4

"And having found the disciples, we tarried there seven days: and these said to Paul through the Spirit, that he should not set foot in Jerusalem." — Acts 21:4 (ASV)

And when they had found disciples. Though the number of the faithful was small, yet some seed of the gospel came there, according to the prophecies of the prophets (Isaiah 23:18), lest Tyre should be entirely without the blessing of God.

And here, as in other previous places, Luke calls Christians disciples, so that we may know that only those are numbered in the flock of Christ who have embraced His doctrine by faith. For it is a vain and false profession for a person to give their name to Christ and not understand what He teaches or speaks. And let the readers note that Paul stayed seven days at Tyre for no other reason than to strengthen them. So we see that wherever he came, he neglected no occasion to do good.

They said by the Spirit. That is, their speech carried divine confirmation, so that Paul would know that they spoke by the Spirit of prophecy. Surely this was no small temptation to not finish the journey he had undertaken, since the Holy Spirit dissuaded him from it. And this was a very plausible reason to avoid the cross, if he had cared for his own safety, to be drawn back as if by the hand of God.

Nevertheless, he did not cease to press on to where he knew he was called by the Lord. However, a question arises here: how can the brethren dissuade him by the Spirit from doing that which Paul testified he does by the inner leading of the same Spirit? Is the Spirit contrary to Himself, so that He now releases Paul whom He held inwardly bound?

I answer that there are diverse gifts of the Spirit, so it is no wonder if those who excel in the gift of prophecy are sometimes lacking in judgment or strength. The Lord showed these brethren, whom Luke mentions, what was to happen; yet, nevertheless, they do not know what is expedient and what Paul’s calling requires, because the measure of their gift does not reach that far.

And the Lord intended His servant to be admonished for this reason: partly, that through long meditation, he might be better equipped and prepared to suffer whatever might come; and partly, that his constancy might be more clearly seen, since, having been informed by prophecies of the sorrowful event, he nevertheless knowingly and willingly makes haste to endure whatever things would befall him.