(6-10) The Apostle is surprised at their rapid defection. The doctrine to which they had at first given in their adhesion was a doctrine of salvation by grace: they now imagined that they were only hearing a different version of the same truths. A different version? How was that possible? There could not be any second gospel, nor was there really anything of the kind. It was not a new gospel, but only a factious perversion of the old. Those who do this — no matter who they be — are accursed. That, at least, is plain speaking, and no one can accuse it of time-serving.
The Apostle had ended his address to the Galatians abruptly, and now he plunges abruptly, and without more preface, into the midst of his charges against them. He cannot understand their sudden apostasy.