For if I build again. The reply consists of two parts. This is the first part, and informs us that the supposition now made is at variance with his whole doctrine, since he had preached the faith of Christ in such a manner as to connect with it the ruin and destruction of sin. For, as we are taught by John, that Christ came not to build up the kingdom of sin, but "that he might destroy the works of the devil," (1 John 3:8,) so Paul declares, that, in preaching the gospel, he had restoreth true righteousness, in order that sin might be destroyed. It was, therefore, in the highest degree improbable, that the same person who destroyed sin should renew its power; and, by stating the absurdity, he repels the calumny.

For if I build again the things which I destroyed - Paul here uses the first person; but he evidently intends it as a general proposition, and means that if anyone does it he becomes a transgressor. The sense is, that if a man, having removed or destroyed that which was evil, again introduces it or establishes it, he does wrong, and is a transgressor of the Law of God. The particular application here, as it seems to me, is to the subject of circumcision and the other rites of the Mosaic law. They had been virtually abolished by the coming of the Redeemer, and by the doctrine of justification by faith. It had been seen that there was no necessity for their observance, and of that Peter and the others had been fully aware. Yet they were lending their influence again to establish them or to build them up again. They complied with them, and they insisted on the necessity of their observance. Their conduct, therefore, was that of building up again that which had once been destroyed, destroyed by the ministry, and toils, and death of the Lord Jesus, and by the fair influence of his gospel. To rebuild that again; to re-establish those customs, was wrong, and now involved the guilt of a transgression of the Law of God. Doddridge supposes that this is an address to the Galatians, and that the address to Peter closed at the previous verse. But it is impossible to determine this; and it seems to me more probable that this is all a part of the address to Peter; or rather perhaps to the assembly when Peter was present; see the note at Galatians 2:15.

For if I build again the things which I destroyed - If I act like a Jew, and enjoin the observance of the law on the Gentiles, which I have repeatedly asserted and proved to be abolished by the death of Christ, then I build up what I destroyed, and thus make myself a transgressor, by not observing the law in that way in which I appear to enjoin the observance of it upon others.

For if I build again the things which I destroyed,.... Which must be understood not of good things, for formerly he destroyed the faith of the Gospel, at least as much as in him lay, and now he built it up, established, and defended it; in doing which he did no evil, or made himself a transgressor, but the reverse; he showed himself a faithful minister of Christ: but of things not lawful, such as the rites and ceremonies of the law of Moses, which were now abrogated, and he had declared to be so all over the Gentile world; and therefore should he go about to establish these things as necessary to salvation, or teach men to join the observance of them with Christ's righteousness for justification, then, says he,
I make myself a transgressor: for he could not be otherwise, be the case how it would with respect to the abrogation, or non-abrogation of the law; for if the law was not abolished, then he made himself a transgressor of it; by neglecting it himself, and teaching others to do so; and if it was abolished, then it must be criminal in him to enforce the observance of it as necessary to a sinner's justification before God. Now though the apostle transfers this to himself, and spoke in his own person to decline all invidious reflections and characters; yet he tacitly regards Peter, and his conduct, who had been taught by the vision the abrogation of the ceremonial law, and acted accordingly by conversing and eating with the Gentiles, and had declared that law to be an insupportable yoke of bondage, which the Gentiles were not obliged to come under; and yet now, by his practice and example, built up and established those very things he had before destroyed, and therefore could not exculpate himself, from being a transgressor: or these things may regard sins and immoralities in life and conversation; and the apostle's sense be, that should he, or any other, take encouragement to sin from the doctrine of free justification by the righteousness of Christ, as if he was the author and minister of sin, and allowed persons in it; this would be to establish sin, which the righteousness of Christ justifies from, and engage in a living in sin, to which, by Christ's righteousness, they are dead unto; than which, nothing can be, a greater contradiction, and which must unavoidably make them not only transgressors of the law, by sinning against it, but apostates, as the word here used signifies, from the Gospel; such must act quite contrary to the nature, use, and design of the Gospel in general, and this doctrine in particular, which teaches men to deny ungodliness and worldly lusts, and that being dead to sin, they should live unto righteousness.

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 (Galatians 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 Galatians 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.

By no means. For if I build again - By my sinful practice. The things which I destroyed - By my preaching, I only make myself - Or show myself, not Christ, to be a transgressor; the whole blame lies on me, not him or his gospel. As if he had said, The objection were just, if the gospel promised justification to men continuing in sin. But it does not. Therefore if any who profess the gospel do not live according to it, they are sinners, it is certain, but not justified, and so the gospel is clear.