16 For God even preferred that His own prediction should fall to the ground, so that the city should not fall. Or rather, the prophecy did not even so fall to the ground. For if indeed while the men continued in the same wickedness, the sentence had not taken effect, some one perhaps might have brought a charge against what was uttered. But if when they had changed, and desisted from their iniquity, God also desisted from His wrath, who shall be able any longer to find fault with the prophecy, or to convict the things spoken of falsehood.
The same law indeed which God had laid down from the beginning, publishing it to all men by the prophet, was on that occasion strictly observed. What then is this law? “I shall speak a sentence,” says He, “concerning a nation or a kingdom, to pluck up, and to pull down, and to destroy it; and it shall be, that if they repent of their evil, I will also repent of the wrath which I said I would do unto them.” Guarding then this law, he saved those who were converted and released from His wrath those who desisted from their wickedness.
He knew the virtue of the barbarians; therefore He hastened the prophet there. Thus was the city agitated at the time, when it heard the prophet's voice, but instead of being injured it was benefited by fear. For that fear was the cause of its safety. The threatening effected the deliverance from the peril. The sentence of overthrow put a stop to the overthrow. O strange and astonishing event! The sentence threatening death, brought forth life! The sentence after it was published became cancelled; the very opposite to that which takes place among temporal judges!
For in their case the proclamation of the sentence causes it to become valid, is fully to ratify it; but on the contrary, with God, the publication of the sentence, caused it to be cancelled. For if it had not been published, the offenders would not have heard; and if they had not heard, they would not have repented, and if they had not repented, they would not have warded off the punishment, nor would they have obtained that astonishing deliverance. For how is it less than astonishing, when the judge declares sentence, and the condemned discharge the sentence by their repentance!
They, indeed, did not flee from the city as we are now doing, but remaining in it they caused it to stand. It was a snare, and they made it a fortification! It was a gulph, and a precipice, and they turned it into a tower of safety! They had heard that the buildings would fall, and yet they fled not from the buildings, but they fled from their sins. They did not depart each from his house as we do now, but each departed from his evil way; for, said they, “why should we think the walls have brought forth the wrath? We are the causes of the wound; we then should provide the medicine.” Therefore they trusted for safety, not to a change of habitations, but of habits.
Source: Homilies on the Statues (New Advent)