Галатам 2:18

Greek, "For if the things which I overthrew (by the faith of Christ), those very things I build up again (namely, legal righteousness, by subjecting myself to the law), I prove myself (literally, 'I commend myself') a transgressor." Instead of commending yourself as you sought to do (Gal 2:12, end), you merely commend yourself as a transgressor. The "I" is intended by Paul for Peter to take to himself, as it is his case, not Paul's own, that is described. A "transgressor" is another word for "sinner" (in Gal 2:17), for "sin is the transgression of the law." You, Peter, by now asserting the law to be obligatory, are proving yourself a "sinner," or "transgressor," in your having set it aside by living as the Gentiles, and with them. Thus you are debarred by transgression from justification by the law, and you debar yourself from justification by Christ, since in your theory He becomes a minister of sin.

The apostle, in this chapter, continues the relation of his past life and conduct, which he had begun in the former; and, by some further instances of what had passed between him and the other apostles, makes it appear that he was not beholden to them either for his knowledge of the gospel or his authority as an apostle, as his adversaries would insinuate; but, on the contrary, that he was owned and approved even by them, as having an equal commission with them to this office. I. He particularly informs them of another journey which he took to Jerusalem many years after the former, and how he behaved himself at that time (Gal 2:1-10). And, II. Gives them an account of another interview he had with the apostle Peter at Antioch, and how he was obliged to behave himself towards him there. From the subject-matter of that conversation, he proceeds to discourse on the great doctrine of justification by faith in Christ, without the works of the law, which it was the main design of this epistle to establish, and which he enlarges more upon in the two following chapters.

2:18 I am a sinner (or lawbreaker): Turning away from faith and back to the law brings a person under the jurisdiction of the law, where all stand under God’s judgment (Rom 3:10-12, 23-24; see Heb 6:1-8), and is itself a serious sin against Christ (Gal 5:2-4; cp. Heb 6:4-6). See also study note on 2:19. • if I rebuild: By insisting on keeping Jewish laws concerning food and circumcision (Gal 2:11-13). • Christ tore down the system of law through his death (Eph 2:14-16).