John Chrysostom
See how he always forestalls the suspicion of supposed self-praise. For nothing so offends the ears of listeners as the recounting of something great and extraordinary about oneself.
But since he was compelled to say something of this kind about himself, he corrects himself, saying: "We do this for you, not for ourselves, so that you may have something in which to boast, not we." Yet even this is not without purpose, but because of the false apostles. Therefore he adds: "those who boast in face and not in heart."
Do you see how he drew them away from the false apostles and brought them to his own side? He showed that the Corinthians themselves wished to have an occasion to defend him and answer those who reproached him.
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"We say this," he says, "not so that we may be praised, but so that you may speak freely on our behalf." This also proves his great love for them. "Nor is it only so that you may boast, but so that you may no longer be deceived."
He did not say this openly, but expressed the same thing in other, more moderate words, without reproaching them. He said: "that you may have" something in which to boast "against those who boast in face."
He commands them to do this not simply and without any need, but when the false apostles exalt themselves. For everywhere he adapts himself to circumstances.
Thus he says this not for his own glory, but to stop the mouths of the false apostles, who boast of their works to the harm of the Corinthians. What does "in face" mean? To boast in outward deeds performed for show.
The false apostles really were such, and they did everything from love of honor. Being empty in soul, although they had the appearance of piety and seemed worthy of honor, they were strangers to good works.