John Calvin Commentary Acts 12:15

"And they said unto her, Thou art mad. But she confidently affirmed that it was even so. And they said, It is his angel." — Acts 12:15 (ASV)

When he did knock at the gate. While they think that the maid is mad, who tells them that Peter had come, we gather from this that they did not hope for or expect Peter’s deliverance. Yet we will not say that they prayed without faith, because they looked for some other success: namely, that Peter, being armed with power from heaven, would be ready, whether by life or by death, to glorify God; that the flock, terrified by the violent invasion of wolves, might not be scattered abroad; that those who were weak might not faint; and that the Lord would remove that whirlwind of persecution.

But in that the Lord grants them more than they hoped for, he surpasses their desires with his infinite goodness. And now what was done seems incredible to them, so that they may be all the more moved to praise his power.

It is his angel. They call him his angel, who was appointed by God to be his keeper and the minister of his safety. In this sense Christ says that the angels of little ones do always see the face of his Father (Matthew 18:10). And what do people commonly gather from this? That every particular person has a particular angel who takes charge of him; but that is too weak a basis.

For Scripture sometimes testifies (Exodus 14:10) that one angel is given to a great people, and a great host to only one man. For Elisha’s servant had his eyes opened, so that he saw in the air chariots of fire, which were appointed to defend the prophet (2 Kings 6:17). And in Daniel, only one angel of the Persians and one of the Grecians is named (Daniel 10:5, 12). Neither does Scripture promise to every person a certain and particular angel, but rather that the Lord has charged his angels to keep all the faithful (Psalms 91:11); also that they pitch their tents around the godly (Psalms 34:8). Therefore, that vain conjecture which is common concerning the two angels for every person is profane.

Let this be sufficient for us: that the whole host of heaven watches for the safety of the Church, and that as the necessity of the time requires, sometimes one angel, sometimes more, defend us with their aid. Assuredly, this is the inestimable goodness of God, in that he says that the angels, who are the beams of his brightness, are our ministers.