New Defender's Study Bible Notes
1:6 another gospel. The word “another” in this verse is heteros, meaning “another of a different kind.” That is, any gospel that is not centered on “the grace of Christ” is not just an alternative gospel; it is a false gospel—no gospel at all.
1:7 not another. In verse 7, on the other hand, the word for “another” is allos, which means “another of the same kind.” Galatians 1:6–7 stresses that the so-called gospel that was misleading the Galatians was not really one with just minor variations from the true gospel, but was altogether opposite to it, a false gospel.