They zealously affect you - See 1 Corinthians 12:31 (Greek); 1 Corinthians 14:39. The word used here (Ζηλόω Zēloō), means to be “zealous” toward, that is, for or against any person or thing; usually, in a good sense, to be eager for. Here it means, that the false teachers made a show of zeal toward the Galatians, or professed affection for them in order to gain them as their followers. They were full of ardor, and professed an extraordinary concern for their welfare - as people always do who are demagogues, or who seek to gain proselytes. The object of the apostle in this is, probably, to say, that it was not wholly owing to themselves that they had become alienated from the doctrines which he had taught. Great pains had been taken to do it; and there had been a show of zeal which would be likely to endanger any person.
But not well - Not with good motives, or with good designs.
Yea, they would exclude you - Margin, “Us.” A few printed editions of the New Testament have ἡμᾶς hēmas, “us,” instead of ὑμᾶς humas, “you” - Mill. The word “exclude” here probably means, that they endeavored to exclude the Galatians from the love and affection of Paul. They would shut them out from that, in order that they might secure them for their own purposes. If the reading in the margin, however, should be retained, the sense would be clearer. “They wish to exclude us, that is, me, the apostle, in order that they may have you wholly to themselves. If they can once get rid of your attachment to me, then they will have no difficulty in securing you for themselves.” This reading, says Rosenmuller, is found “in many of the best codices, and versions, and fathers.” It is adopted by Doddridge, Locke, and others. The main idea is clear: Paul stood in the way of their designs. The Galatians were truly attached to him, and it was necessary, in order to accomplish their ends, to withdraw their affections from him. When false teachers have designs on a people, they begin by alienating their confidence and affections from their pastors and teachers. They can hope for no success until this is done; and hence, the efforts of errorists, and of infidels, and of scorners, is to undermine the confidence of a people in the ministry, and when this is done there is little difficulty in drawing them over to their own purposes.
That ye might affect them - The same word as in the former part of the verse, “that ye might zealously affect them” - that is, that ye might show ardent attachment to them. Their first work is to manifest special interest for your welfare; their second, to alienate you from him who had first preached the gospel to you; their object, not your salvation, or your real good, but to secure your zealous love for themselves.