Titus 2:1

ii. 1. "But speak thou the things that become sound doctrine." This then is uncleanness. They are themselves unclean. But be not thou silent on that account. Do thy part, although they may not receive thee. Advise and counsel them, though they may not be persuaded. Here he censures them more severely. For they who are mad imagine that nothing stands still, yet this arises not from the objects that are seen, but from the eyes that see. Because they are unsteady and giddy, they think that the earth turns round with them, which yet turns not, but stands firm. The derangement is of their own state, not from any affection of the element. So it is here, when the soul is unclean, it thinks all things unclean. Therefore scrupulous observances are no mark of purity, but it is the part of purity to be bold in all things. For he that is pure by nature ventures upon all things, they that are defiled, upon nothing. This we may say against Marcion. Seest thou that it is a mark of purity to be superior to all defilement, to touch nothing implies impurity. This holds even with respect to God. That He assumed flesh is a proof of purity; if through fear He had not taken it, there would have been defilement. He who eats not things that seem unclean, is himself unclean and weak, he who eats, is neither. Let us not call such pure, they are the unclean. He is pure, who dares to feed upon all things. All this caution we ought to exercise towards the things that defile the soul. For that is uncleanness, that is defilement. None of these things is so. Those who have a vitiated palate think what is set before them is unclean, but this is the effect of their disorder. It becomes us therefore to understand the nature of things pure, and things unclean.