John Chrysostom
This was said not to free them from shame, but to anticipate them with praises and keep them in obedience by a multitude of witnesses.
I alone do not bear witness, he says, but the whole world. The Apostle did not say, “your prudence,” but, “your obedience,” that is, submission.
This testified to great meekness. “I rejoice over you.” This too is no small praise.
Then after the praise comes exhortation. Having freed them from accusation, the Apostle again gives them hints, lest through forgetfulness they become more negligent.
He says, “I want you to be wise in what is good and simple in what is evil.” Do you see how subtly he reproves them again, when they do not suspect it?
By this the Apostle hints that some of them have already been deceived.