John Chrysostom

"And lest when I come again, my God should humble me among you." And the word "again," too, is as smiting them. For he means, 'What happened before is enough;' as he said also in the beginning [of the Epistle], "to spare you, I came not as yet to Corinth." Seest thou how he shows both indignation and tender affection? But what means, "will humble me?" And yet this is glorious rather, to accuse, to take vengeance, to call to account, to be seated in the place of judge; howbeit he calls it a humbling. …

Homily 28 on 2 Corinthians ↗

Theophylact of Ohrid

That is, the above said is sufficient, and I am afraid that, having come to you, I will be compelled to deal with you severely. By humiliation, then, he means the necessity of strongly punishing someone, although many consider this an honor for themselves. And he did not say "lest I be humiliated," but "lest my God humiliate me," showing that he would do this for the sake of God. And if the matter did not concern God and His commandments, he himself would not have appeared so severe. …

Commentary on 2 Corinthians ↗

Cyprian

And yet to these persons themselves repentance is granted, and the hope of lamenting and atoning is left, according to the saying of the same apostle: "I fear lest, when I come to you, I shall bewail many of those who have sinned already, and have not repented of the uncleanness, and fornication, and lasciviousness which they have committed.". …

Epistle LI ↗

Thomas Aquinas

Then he manifests their wickedness in regard to past evils for which they have not repented, when he says: I fear that when I come again my God may humble me, i.e., afflict me, before you and I may have to mourn over many of those who sinned before, i.e., before the first epistle. And rightly do I mourn, because just as the glory of the father is in the glory of his children, so the father's shame is the shame of the children. …

Commentary on 2 Corinthians ↗