Athanasius of Alexandria

Thus [the devil] suffers and is dishonored; and although he still ventures with shameless confidence to disguise himself, yet now, wretched spirit, he is detected rather by those who bear the sign on their foreheads; and he is even rejected by them, and is humbled and put to shame. For even if, now that he is a creeping serpent, he shall transform himself into an angel of light, yet his deception will not profit him; for we have been taught that “though an angel from heaven preach to us any other gospel than that we have received, he is anathema.”

What then has persuaded you to contradict each other and to procure to yourselves so great a disgrace? You cannot give any good account of it; this supposition only remains, that all you do is but outward profession and pretense.… And you make nothing of accusing the Fathers, and you complain outright of the expressions as being unscriptural; and, as it is written, “opened your legs to every one that passed by;” so as to change as often as they wish, in whose pay and keep you are. Yet, though a person uses terms not in Scripture, it makes no difference, so that his meaning is religious. But the heretic, though he uses scriptural terms, because he is equally dangerous and depraved, will be asked in the words of the Spirit, “Why do you preach my laws and take my covenant in your mouth?”