Galatians 1:9

9.As we said before. Leaving out, in this instance, the mention of himself and of angels, he repeats the former assertion, that it is unlawful for any man to teach anything contrary to what they had learned. (23) Observe the expression — ye have received; for he uniformly insists, that they must not regard the gospel as something unknown, existing in the air, or in their own imaginations. He exhorts them to entertain a firm and serious conviction, that the doctrine which they had received and embraced is the true gospel of Christ. Nothing can be more inconsistent with the nature of faith than a feeble, wavering assent. What, then, must be the consequence, if ignorance of the nature and character of the gospel shall lead to hesitation? Accordingly he enjoins them to regard as devils those who shall dare to bring forward a gospel different from his, — meaning by another gospel, one to which the inventions of other men are added; (24) for the doctrine of the false apostles was not entirely contrary, or even different, from that of Paul, but corrupted by false additions.

To what poor subterfuges do the Papists resort, in order to escape from the Apostle’s declaration! First, they tell us, that we have not in our possession the whole of Paul’s preaching, and cannot know what it contained, unless the Galatians who heard it shall be raised from the dead, in order to appear as witnesses. Next, they assert, that it is not every kind of addition which is forbidden, but that other gospels only are condemned. What Paul’s doctrine was, so far as it concerns us to know, may be learned with sufficient clearness from his writings. Of this gospel, it is plain, the whole of Popery is a dreadful perversion. And from the nature of the case, we remark in conclusion, it is manifest that any spurious doctrine whatever is at variance with Paul’s preaching; so that these cavils will avail them nothing.