[8.] Let us then learn this lesson. Do not, when thou hearest that a man is not a Heathen nor a Jew, straightway believe him to be a Christian; but examine also into all the other points; for even Manichæans, and all the heresies, have put on this mask, in order thus to deceive the more simple. But if we “have the senses” of the soul “exercised to discern both good and evil,” we are able to discern such [teachers].