Do you mark what happened in the former case, and what here? There a girl was released from a spirit, and they cast them into prison, because they had liberated her from the spirit. Here, they did but show the doors standing open, and it opened the doors of his heart, it loosed two sorts of chains; that (prisoner) kindled the (true) light; for the light in his heart was shining. “And he sprang in, and fell before them;” and he does not ask, How is this? What is this? But straightway he says, “What must I do to be saved?”
What then answers Paul? “Believe in the Lord Jesus Christ, and you shall be saved, you and your house.” For this above all, wins men: that one's house also should be saved. “And they spoke the word to him, and to all that were in his house. And he took them the same hour of the night, and washed their stripes,” etc. (<!--<span class="stiki"></span>-->v. 32, 33), washed them and was washed: those he washed from their stripes, himself was washed from his sins: he fed and was fed. “And rejoiced,” it says: although there was nothing but words only and good hopes: having believed in God with all his house: this was the token of his having believed— that he was released of all.
What worse than a jailer, what more ruthless, more savage? He entertained them with great honor. Not, because he was safe, he made merry, but, having believed God. (a) “Believe in the Lord,” said the Apostle: therefore it is that the writer here says, “Having believed. — (d) Now therefore,” it says, “depart, and go in peace”: that is, in safety, fearing no man. (b) “But Paul said unto them”: that he may not seem to be receiving his liberty as one condemned, and as one that has done wrong: therefore it is that he says, “Having openly beaten us uncondemned,” etc.— that it may not be matter of grace on their part.
(e) And besides, they wish the jailer himself to be out of danger, that he may not be called to account for this afterwards. And they do not say, “Having beaten us,” who have wrought miracles: for they (the magistrates) did not even heed these: but, that which was most effectual to shake their minds, “uncondemned, and being Romans.” (c) Observe how diversely grace manages things: how Peter went out, how Paul, though both were Apostles. “They feared,” it says: because the men were Romans, not because they had unjustly cast them into prison, “And besought them to depart out of the city”: begged them as a favor.
And they went to the house of Lydia, and having confirmed her, so departed. For it was not right to leave their hostess in distress and anxiety. But they went out, not in compliance with the request of those rulers, but hasting to the preaching: the city having been sufficiently benefited by the miracle: for it was fit they should not be there any longer. For in the absence of them that wrought it, the miracle appeared greater, itself crying out more loudly: the faith of the jailer was a voice in itself. What equal to this? He is put in bonds, and looses, being bound: looses a twofold bond: him that bound him, he looses by being bound. These are indeed works of (supernatural) grace.
Source: Homilies on Acts (New Advent)