5. But he answers, "What did Paul find to criticize in Peter?" What else but what he said himself, what he wrote himself? He himself composed a letter as a record, he left it to posterity to be read in the Church. What can I safely believe in the divine books, if I don't believe what is written in that letter? It's an apostolic letter, it's a canonical letter. It's a letter from Paul, who labored more than them all; not he, though, but the grace of God with him (1 Cor 15:10). So it's a letter from the grace of God. And if we recall who was speaking in him, it's a letter from Christ. Or do you wish, he says, to have experience of the one who is speaking in me, Christ? (2 Cor 13:3). Listen, and fear. He said "experience," not a pretense. But if you don't think that's enough, listen to his own public assertion, in which he even calls God to witness. This is how he started the tale of what he was going to point out, as though foreseeing that there would be some people who queried the truth of it: But what I am writing to you, he said, see before God that I am not lying (Gal. 1:20). So then, when he calls God to witness like that, is he lying, seeing that without any calling of God to witness the mouth that lies, it says, will kill, not the body, but the soul (Wis 1:11)? I beg you, don't let Paul be killed in the soul for Peter's sake; they were both killed together in the flesh for Christ's sake.Augustine, Sermon 162C, Section 5 (The Works of Augustine, Sermons III/11, New City Press, 1997, p. 169)
I realize that a few people are going to read everything Augustine said in that section and home in on the allusion to Wisdom 1:11, losing track of everything else that was said. I hope that if you're one of those people you'll think about re-reading the paragraph, setting that issue aside. Although Augustine does seem to allude to (or even quote from) a verse from the Book of Wisdom, he doesn't identify that book as the canonical Scriptures here. Instead, the canonical Scriptures being discussed here are Paul's own epistle to the Galatians.