Jamieson, Fausset and Brown on Galatians 1:7

7. another--A distinct Greek word from that in Ga 1:6. Though I called it a gospel (Ga 1:6), it is not really so. There is really but one Gospel, and no other gospel.

but--Translate, "Only that there are some that trouble you," &c. (Ga 5:10, 12). All I meant by the "different gospel" was nothing but a perversion by "some" of the one Gospel of Christ.

would pervert--Greek, "wish to pervert"; they could not really pervert the Gospel, though they could pervert Gospel professors (compare Ga 4:9, 17, 21; 6:12, 13; Col 2:18). Though acknowledging Christ, they insisted on circumcision and Jewish ordinances and professed to rest on the authority of other apostles, namely, Peter and James. But Paul recognizes no gospel, save the pure Gospel.