[21.] When therefore certain of this sort wandering about provinces and cities, and carrying with them their venal errors, had found their way to Galatia, and when the Galatians, on hearing them, nauseating the truth, and vomiting up the manna of Apostolic and Catholic doctrine, were delighted with the garbage of heretical novelty, the apostle putting in exercise the authority of his office, delivered his sentence with the utmost severity, "Though we," he says, "or an angel from heaven, preach any other Gospel unto you than that which we have preached unto you, let him be accursed." 
[22.] Why does he say "Though we"? why not rather "though I"? He means, "though Peter, though Andrew, though John, in a word, though the whole company of apostles, preach unto you other than we have preached unto you, let him be accursed." Tremendous severity! He spares neither himself nor his fellow apostles, so he may preserve unaltered the faith which was at first delivered. Nay, this is not all. He goes on "Even though an angel from heaven preach unto you any other Gospel than that which we have preached unto you, let him be accursed." It was not enough for the preservation of the faith once delivered to have referred to man; he must needs comprehend angels also. "Though we," he says, "or an angel from heaven." Not that the holy angels of heaven are now capable of sinning. But what he means is: Even if that were to happen which cannot happen, -- if any one, be he who he may, attempt to alter the faith once for all delivered, let him be accursed.
[23.] But it may be, he spoke thus in the first instance inconsiderately, giving vent to human impetuosity rather than expressing himself under divine guidance. Far from it. He follows up what he had said, and urges it with intense reiterated earnestness, "As we said before, so say I now again, If any man preach any other Gospel to you than that ye have received, let him be accursed." He does not say, "If any man deliver to you another message than that you have received, let him be blessed, praised, welcomed," -- no; but "let him be accursed," [anathema] i.e., separated, segregated, excluded, lest the dire contagion of a single sheep contaminate the guiltless flock of Christ by his poisonous intermixture with them.
 Galatians 1:8.