John Calvin Commentary Acts 1:4

"and, being assembled together with them, he charged them not to depart from Jerusalem, but to wait for the promise of the Father, which, [said he], ye heard from me:" — Acts 1:4 (ASV)

Gathering them together, he commanded, etc. They had previously performed the duties of Apostles, but that lasted only a short time. Secondly, it was to the extent that by their preaching they might awaken the Jews to hear their Master. And so that commandment to teach, which Christ had given them (Matthew 10:7) while he lived with them on earth, was, as it were, a certain entrance into their apostleship which was to come, for which they were not yet ready.

Therefore, their ordinary function was not laid upon them until Christ had risen again. Instead, they stirred up their nation (as I have said) like criers, so that they might give ear to Christ. And then finally, after the resurrection, they were made Apostles to publish throughout the whole world the doctrine that was committed to them.

And although after they were made Apostles, Christ still commanded them to abstain from their office, this was done for good reason; indeed, many reasons can be given why it should be so. That despicable forsaking of their Master was still fresh; many signs and indications of unbelief were still fresh.

Since they had been so thoroughly taught and had so suddenly forgotten everything, they showed a clear sign of their great dullness of mind. Nor were they free from sluggishness, which could not be properly purged in any other way than by delaying the promised grace, so that he might sharpen their desire all the more.

But this reason is especially to be noted: the Lord appointed a specific time for the sending of the Spirit, so that the miracle might be more apparent. Again, he allowed them to rest for a while, so that he might better display the greatness of the work he was about to entrust to them. And in this way, the truth of the gospel is confirmed, because the Apostles were forbidden to begin preaching it until they were well prepared in due time.

And they were commanded to stay together, because they were all to have one Spirit given to them. If they had been dispersed, this unity would not have been so well known. Though they were scattered afterwards in various places, yet because they brought what they had received from one and the same source, it was just as if they had always spoken with one voice. Furthermore, it was fitting that they should begin to preach the gospel at Jerusalem, so that the prophecy might be fulfilled:

“There shall a law go out of Zion,
and the word of the Lord out of Jerusalem” (Isaiah 2:3).

Although the participle συναλιζομενος can be translated in various ways, Erasmus's translation pleased me most, because the meaning of gathering together will agree better with the context.

They should wait for the promise. It was fitting that these men, who would shortly after lay Christ’s yoke upon the neck of the world, should first be accustomed to obey. And surely, by their example, they have taught us that we must work and rest only at the Lord’s pleasure.

For if, during our life, we wage spiritual warfare under his banner and leadership, surely he ought to have no less authority over us than any earthly captain has in his army. Therefore, as military discipline requires that no one should engage in battle unless commanded by the captain, so it is not lawful for us either to go out or to attempt anything until the Lord gives the command.

And as soon as he sounds the retreat, we must halt. Moreover, we are taught that we become partakers of God’s gifts through hope.

But we must note the nature of hope as it is described in this place. For that is not hope which everyone devises for himself rashly, but that hope which is grounded on the promise of God. Therefore Christ does not allow his apostles to look for whatever they want, but he expressly adds the promise of the Father.

Furthermore, he makes himself a witness of it, because we ought to be so sure and certain that even if all the forces of hell oppose us, yet this conviction should remain firmly fixed in our minds: that we have believed God. As Paul says, I know whom I have believed (2 Timothy 1:12). And here he reminds them of those things which are written in John 14:15-16:

“I will pray the Father, and he shall give you another Comforter, that he may continue with you; I say the Spirit of truth,” etc.

Again,

“I have spoken these things to you while I am with you. And the Spirit, whom my Father shall send in my name, shall teach you all things” (John 14:25–26), etc.

And again,

“When the Spirit of truth shall come, whom I will send from my Father, he shall bear witness of me” (John 15:26).

And again,

“If I shall go hence, I will send you the Comforter, who shall reprove the world” (John 16:7).

And he had said long before,

“He who believes in me, out of his belly
shall flow rivers of living water” (John 7:38).