16 That this very particular also contributes much to the showing forth of God's power, you may learn even from the same Apostle, who told us the former. In order that you may not say, (what indeed unbelievers think), that God in permitting this, is some infirm being, and suffers such persons to be continually afflicted, from not being able to deliver His own from dangers: this very thing, I say, observe how Paul has demonstrated by means of these events, showing not only that the events were far from accusing Him of weakness, but that they proved His power more strikingly to all.
For having said, “There was given me a thorn in the flesh; a messenger of Satan to buffet me,” and having thus signified his repeated trials, he goes on to add, “For this thing I besought the Lord thrice, that it might depart from me; and He said unto me, My grace is sufficient for you, for My strength is perfected in weakness.” “My power,” He means, “is seen then when you are in weakness; and yet through you, who seem to grow weak, the word preached is magnified, and is sown in all quarters.”
When therefore he was led to the dungeon, after having received a great number of stripes, he took prisoner the keeper of the prison. His feet were in the stocks, and his hands in the chain; and the prison shook at midnight while they were singing hymns. See you, how His power was perfected in weakness? If Paul had been at large, and had shaken that building, the thing would not have been so wonderful. “For this reason,” He says, “remain bound; and the walls shall be shaken on every side, and the prisoners shall be loosed; in order that My power may appear the greater, when through you, confined and in fetters, all that are in bonds shall be loosed.”
This very circumstance then it was which at the time astounded the keeper of the prison, that being so forcibly confined, he, through prayer alone, prevailed to shake the foundations, and throw open the doors of the prison, and to unbind all the prisoners. Nor is this the only occasion. But with Peter too, and Paul himself, as well as the other disciples, one may see this occurring constantly; and in the midst of persecution, the grace of God ever flourishing, and appearing by the side of the tribulations, and thus proclaiming His power. Wherefore He says, “My grace is sufficient for you, for My strength is perfected in weakness.”
Source: Homilies on the Statues (New Advent)