John Chrysostom

"On behalf of such an one will I glory?" wherefore? For if another were caught up, wherefore dost thou glory? Whence it is evident that he said these things of himself. And if he added, "but of myself I will not glory," he says nothing else than this, that, 'when there is no necessity, I will say nothing of that kind fruitlessly and at random;' or else he is again throwing obscurity over what he had said, as best he might. For that the whole discourse was about himself, what follows also clearly shows.

Homily 26 on 2 Corinthians ↗

Theophylact of Ohrid

Notice his humility: he recounts this as if about someone else, for he says, "of such a one I will boast." But if it was another who was caught up, then why do you boast? So then, it is evident that he says this about himself. He says this either in order to show that he would not have spoken of it without necessity, or, as one may suppose, in order to make his speech veiled. That is, by afflictions, by persecutions.

Commentary on 2 Corinthians ↗

Thomas Aquinas

Then when he says, On behalf of this man I will boast, he shows how he reacted to this glory. In regard to this he does three things. First, he shows that he did not glory in such revelations; secondly, he suggests that he has something else in which to glory (v. 6). In regard to the first it should be noted that the statement, on behalf of this man I will boast [glory], but on my own behalf I will not boast, can be read in two ways. …

Commentary on 2 Corinthians ↗