Verse 1-10 — Observe the apostle's faithfulness in giving a full account of the doctrine he had preached among the Gentiles, and was still resolved to preach, that of Christianity, free from all mixture of Judaism. This doctrine would be ungrateful to many, yet he was not afraid to own it. His care was, lest the success of his past labours should be lessened, or his future usefulness be hindered. While we simply depend upon God for success to our labours, we should use every proper caution to remove mistakes, and against opposers. There are things which may lawfully be complied with, yet, when they cannot be done without betraying the truth, they ought to be refused. We must not give place to any conduct, whereby the truth of the gospel would be reflected upon. Though Paul conversed with the other apostles, yet he did not receive any addition to his knowledge, or authority, from them. Perceiving the grace given to him, they gave unto him and Barnabas the right hand of fellowship, whereby they acknowledged that he was designed to the honour and office of an apostle as well as themselves. They agreed that these two should go to the heathen, while they continued to preach to the Jews; judging it agreeable to the mind of Christ, so to divide their work. Here we learn that the gospel is not ours, but God's; and that men are but the keepers of it; for this we are to praise God. The apostle showed his charitable disposition, and how ready he was to own the Jewish converts as brethren, though many would scarcely allow the like favour to the converted Gentiles; but mere difference of opinion was no reason to him why he should not help them. Herein is a pattern of Christian charity, which we should extend to all the disciples of Christ.
Verse 11-14 — Notwithstanding Peter's character, yet, when Paul saw him acting so as to hurt the truth of the gospel and the peace of the church, he was not afraid to reprove him. When he saw that Peter and the others did not live up to that principle which the gospel taught, and which they professed, namely, That by the death of Christ the partition wall between Jew and Gentile was taken down, and the observance of the law of Moses was no longer in force; as Peter's offence was public, he publicly reproved him. There is a very great difference between the prudence of St. Paul, who bore with, and used for a time, the ceremonies of the law as not sinful, and the timid conduct of St. Peter, who, by withdrawing from the Gentiles, led others to think that these ceremonies were necessary.
Verse 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.