2:15-19 Paul, having thus shown he was not inferior to any apostle, not to Peter himself, speaks of the great foundation doctrine of the gospel. For what did we believe in Christ? Was it not that we might be justified by the faith of Christ? If so, is it not foolish to go back to the law, and to expect to be justified by the merit of moral works, or sacrifices, or ceremonies? The occasion of this declaration doubtless arose from the ceremonial law; but the argument is quite as strong against all dependence upon the works of the moral law, as respects justification. To give the greater weight to this, it is added, But if, while we seek to be justified by Christ, we ourselves also are found sinners, is Christ the minister of sin? This would be very dishonourable to Christ, and also very hurtful to them. By considering the law itself, he saw that justification was not to be expected by the works of it, and that there was now no further need of the sacrifices and cleansings of it, since they were done away in Christ, by his offering up himself a sacrifice for us. He did not hope or fear any thing from it; any more than a dead man from enemies. But the effect was not a careless, lawless life. It was necessary, that he might live to God, and be devoted to him through the motives and grace of the gospel. It is no new prejudice, though a most unjust one, that the doctrine of justification by faith alone, tends to encourage people in sin. Not so, for to take occasion from free grace, or the doctrine of it, to live in sin, is to try to make Christ the minister of sin, at any thought of which all Christian hearts would shudder.
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 (Ga 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 Ga 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.