John Calvin Commentary Acts 16:29

"And he called for lights and sprang in, and, trembling for fear, fell down before Paul and Silas," — Acts 16:29 (ASV)

Being astonished, he fell down. This keeper was compelled by fear to show obedience to God, just as much as he was by the miracle that prepared him for it. By this it appears what a good thing it is for people to be thrown down from their pride, so that they may learn to submit themselves to God.

He was hardened in his superstitions; therefore, he might, with a proud spirit, have despised whatever Paul and Silas might have said, whom he had reproachfully thrust into the innermost part of the prison. Now, fear makes him teachable and gentle. Therefore, whenever the Lord strikes us or casts us down, let us know that this is done so that we may be brought to order from our excessive pride.

But it is surprising that he was not rebuked for falling down at their feet. For why did Paul overlook that which, as Luke records (Acts 10:26), Peter would not allow in Cornelius? I answer that Paul therefore tolerates the keeper because he knows that he was not motivated by superstition, but by fear of God’s judgment to humble himself in this way.

It was a common enough kind of worship; but especially among the Romans, it was an established custom when they wanted to humbly ask for something, or ask for pardon, that they fell down at the knees of those to whom they made their request. Therefore, there was no reason why Paul should be displeased with a man whom he saw as simply humbled by God.

For if anything had been done contrary to the glory of God, he would not have forgotten the zeal he showed previously among the men of Lycaonia. Therefore, by his silence, we conclude that in this kind of worship there was nothing contrary to godliness or the glory of God.