Abstain from every form of evil.
In the first place, the phrase appearance of evil, or evil appearance, I understand to mean — when falsity of doctrine has not yet been discovered in such a manner, that it can on good grounds be rejected; but at the same time an unhappy suspicion is left upon the mind, and fears are entertained, lest there should be some poison lurking. He, accordingly, commands us to abstain from that kind of doctrine, which has an appearance of being evil, though it is not really so — not that he allows that it should be altogether rejected, but inasmuch as it ought not to be received, or to obtain belief. For why has he previously commanded that what is good should be held fast, while he now desires that we should abstain not simply from evil, but from all appearance of evil? It is for this reason, that, when truth has been brought to light by careful examination, it is assuredly becoming in that case to give credit to it. When, on the other hand, there is any fear of false doctrine, or when the mind is involved in doubt, it is proper in that case to retreat, or to suspend our step, as they say, lest we should receive anything with a doubtful and perplexed conscience. In short, he shews us in what way prophecy will be useful to us without any danger — in the event of our being attentive in proving all things, and our being free from lightness and haste. 