John Calvin on Acts 4:31

31. And when they had prayed. Luke declareth now that God did not only hear this prayer, but did also testify the same by a visible sign from heaven. For the shaking of the place should, of itself, have done them small good; but it tendeth to another end, that the faithful may know that God is present with them. Finally, it is nothing else but a token of the presence of God. But the fruit followeth, for they are all filled with the Holy Ghost, and endowed with greater boldness. We ought rather to stand upon this second member. For whereas God did declare his power then by shaking the place it was a rare and extraordinary thing; and whereas it appeared by the effect, that the apostles did obtain that which they desired, this is a perpetual profit of prayer, which is also set before us for an example.

Acts 4:32-37

32. And the multitude which believed had one heart and one soul; and no man did say that any of those things which he possessed was his own; but they had all things common. 33. And the apostles did bear witness of the resurrection of Jesus Christ with great power; and great grace was upon them all. 34. For there was one among them that kicked: for so many as possessed lands or houses, setting them, they brought the price of those things which were sold, 35. And they laid it at the feet of the apostles: and it was distributed to every man according as he had need. 36. And Joses, which was suremined of the opostles Barnabas, (which is, the son of comfort,) a Levite, of the country of Cyprus, 37. Whereas he had land, he sold it, and brought the money, and laid it at the apostles’ feet.