4:12-18 The apostle desires that they would be of one mind with him respecting the law of Moses, as well as united with him in love. In reproving others, we should take care to convince them that our reproofs are from sincere regard to the honour of God and religion and their welfare. The apostle reminds the Galatians of the difficulty under which he laboured when he first came among them. But he notices, that he was a welcome messenger to them. Yet how very uncertain are the favour and respect of men! Let us labour to be accepted of God. You once thought yourselves happy in receiving the gospel; have you now reason to think otherwise? Christians must not forbear speaking the truth, for fear of offending others. The false teachers who drew the Galatians from the truth of the gospel were designing men. They pretended affection, but they were not sincere and upright. An excellent rule is given. It is good to be zealous always in a good thing; not for a time only, or now and then, but always. Happy would it be for the church of Christ, if this zeal was better maintained.
17. They—your flatterers: in contrast to Paul himself, who tells them the truth.
zealously—zeal in proselytism was characteristic especially of the Jews, and so of Judaizers (Ga 1:14; Mt 23:15; Ro 10:2).
affect you—that is, court you (2Co 11:2).
not well—not in a good way, or for a good end. Neither the cause of their zealous courting of you, nor the manner, is what it ought to be.
they would exclude you—"They wish to shut you out" from the kingdom of God (that is, they wish to persuade you that as uncircumcised Gentiles, you are shut out from it), "that ye may zealously court them," that is, become circumcised, as zealous followers of themselves. Alford explains it, that their wish was to shut out the Galatians from the general community, and attract them as a separate clique to their own party. So the English word "exclusive," is used.