John Chrysostom

Having said, "I do not regret," he tells the reason also; alleging the good that resulted from his letter; and skillfully excusing himself by saying, "though but for a season." For truly that which was painful was brief, but that which was profitable was perpetual. …

Homily 15 on 2 Corinthians ↗

Theophylact of Ohrid

Although I wrote to you in such a way, he says, that I exceeded the measure of reproach and ought to have repented of having censured you beyond measure, yet the great benefit arising from it does not allow me now to repent. He said this not because he had in fact censured them beyond measure, but in order to increase their praise.

Commentary on 2 Corinthians ↗

Augustine of Hippo

Moreover, even sorrow, the emotion for which, the Stoics claim, there can be found in the soul of a wise man no corresponding "attitude," is a word used in a good sense, especially in Christian writings. The apostle, for example, praises the Corinthians because they were sorrowful according to God. Of course, someone may object that the apostle congratulated the Corinthians because their sorrow led them to repentance and that such sorrow can be experienced only by those who have sinned. …

City of God 14.8 ↗

Thomas Aquinas

For they had sinned by fornication, and the Apostle has rebuked them, as is evident from the first epistle (chaps. 5-6). But at that time he wondered what effect that sadness would have, whether good or bad; therefore, in his wonder he felt sad. But later, seeing that good had come from it, he was glad. Hence, he says: For even if I made you sorry with my letter, I do not regret it now, because you have been corrected. …

Commentary on 2 Corinthians ↗