John Chrysostom

But what? "That ye should do that which is honorable," we pray for this, that ye should ever live in virtue, ever in amendment; "and we should be as reprobate," not displaying our power of punishing. And he said not, "reprobate" for he would not "be" reprobate, even though he did not punish, nay rather for this very reason he would be "approved;" "but even if some suspect us," he says, "on account of our not displaying our power, to be contemptible and cast away, we care nothing for this. …

Homily 29 on 2 Corinthians ↗

Theophylact of Ohrid

Note his mercy. He was despised, reviled as a man having no power and only boasting in writing; yet he not only cancels the punishment, but even implores them not to sin, so as not to bring him to the necessity of punishing. For I am not striving to appear "what I ought to be" and as one having the power to punish, but that you should always do good and repent if you sin; and let me be considered "not what I ought to be," that is, let me seem to many to be weak and powerless, as one who found no occasion to punish you. …

Commentary on 2 Corinthians ↗

Thomas Aquinas

Then when he says, But we pray God, he excludes the suspicion. For he had threatened them with a severe judgment when he mentioned his power to judge, and suggested an examination, trusting that Christ was in them, unless they were reprobate. Nevertheless he leaves in doubt the question whether Christ be in them. …

Commentary on 2 Corinthians ↗