John Chrysostom
Then, so that they would not think he says this to win greater goodwill from them, he adds: "The truth of Christ is in me" (v. 10). "Do not think that I say this with the intention of receiving something or drawing you more strongly to myself. By the truth of Christ in me," he says, "I say that this boasting shall not be stopped for me in the regions of Achaia."
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Again, lest someone think that he is grieving over this or speaking so in anger, he calls his act a boast. Likewise in the first epistle, he does not speak there to insult them: "What then is my reward? That in preaching the Gospel I may proclaim the Gospel of Christ without charge" (2 Cor. 9:18). As in the first epistle he calls this a reward, so here he calls it a boast, so as not to shame them too greatly by his words, as though they had not provided for him although he had asked. "What then?" he says. "You too would be ready to give, but I do not take."
The words "shall not be taken away," or "shall not be stopped," are used figuratively. They are taken from a river that is dammed, and mean that his glory, that he does not take, spreads everywhere like a river. "You will not stop my freedom by your almsgiving." Yet he did not say, "You will not take it away," or "you will not stop it," which would have been harsher for them. Instead he says, "It shall not be taken away from me in the regions of Achaia."
This again could have struck them terribly and was quite sufficient to cast them into despondency and sorrow, namely, that he rejects them alone. Indeed, if he boasts in this, he ought to boast everywhere. But if he boasts only among you, perhaps it is because of your weakness.