John Calvin Commentary Galatians 5:8

"This persuasion [came] not of him that calleth you." — Galatians 5:8 (ASV)

This persuasion cometh not. Having formerly combated them with arguments, he finally pronounces, with a voice of authority, that their persuasion did not come from God. Such an admonition would not be entitled to much regard if it were not supported by the authority of the speaker. But Paul, to whom the Galatians had been indebted for the announcement of their Divine calling, was well entitled to address them in this confident language.

This is the reason why he does not directly say, from God, but expresses it by a circumlocution, him that hath called you. As if he had said, “God is never inconsistent with himself, and it is he who by my preaching called you to salvation. This new persuasion then has come from some other source; and if you wish your calling to be considered as from God, beware of lending an ear to those who thrust upon you their new inventions.” Though the Greek participle καλοῦντος, I acknowledge, is in the present tense, I have preferred translating, who hath called you, in order to remove the ambiguity.