John Chrysostom
What does he express here by the words "to have confidence" and "in the flesh"? He means boasting about oneself, boldness, and importance. He added this well.
If he, being from the Gentiles, had disparaged circumcision, and not circumcision only, but also those who receive it out of season, it would have seemed that he attacked it because he lacked noble Jewish origin. It would have seemed that he did not know its great advantages and had no share in them.
But when he has a share and disparages it, he does so not because he lacks a share, but because he does not recognize its value. He does this not from ignorance, but from perfect knowledge.
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See what he says also in the Epistle to the Galatians, when he is compelled to set forth his own merits. See how at the same time he shows humility of mind. "You have heard," he says, "of my former way of life in Judaism" (Gal 1:13).
And again here, "If anyone else thinks he may have confidence in the flesh, I more so." He immediately adds, "a Hebrew of Hebrews." He did not say this before, but only after the words "if anyone else." By this he shows the necessity, and shows that he spoke for their sake.
If you too have confidence, he says, then I have more. I say this now; otherwise I would have kept silent.
Notice the gentleness of his reproofs. By reproving impersonally, he gives them a way to escape the rebuke. "If anyone else thinks he may have confidence." He said well, "thinks," either because they did not have such confidence, or because their confidence was not true confidence. For everything was a matter of necessity, not of free will.