A different gospel, which is not another (1:6–7)

Says Galatians 1:6 opens Θαυμάζω (Thaumazō, “I am amazed”). The verb μετατίθεσθε (metatithesthe) is present middle of μετατίθημι, glossed “to change oneself, pass over” with ἀπό and εἰς at this verse; the present tense describes the turning as under way (BSB “are deserting”). They are turning ἀπὸ τοῦ καλέσαντος ὑμᾶς, from the one who called them, εἰς ἕτερον εὐαγγέλιον.

Says Galatians 1:7 adds ὃ οὐκ ἔστιν ἄλλο (ho ouk estin allo, “which is not another”). For ἕτερος, Abbott-Smith lists this verse under “Of kind or quality, other, another, different”; under ἄλλος he notes that “ἄ. denotes numerical, ἕ. qualitative difference”, citing comment on Galatians 1:6–7. The verse then names οἱ ταράσσοντες ὑμᾶς (ταράσσω, “to trouble, disquiet, perplex”) who want μεταστρέψαι τὸ εὐαγγέλιον τοῦ Χριστοῦ (metastrepsai to euangelion tou Christou), where μεταστρέφω is glossed “to pervert, corrupt”.

Implies The relative clause denies that the “different” message is a second gospel at all; the BSB “which is not even a gospel” gives that sense. εἰ μή (“except that”) then explains the only reality behind it: people who trouble the readers and want to turn the one gospel of Christ into something else.