1 I had frequently, Demetrianus, treated with contempt your railing and noisy clamour with sacrilegious mouth and impious words against the one and true God, thinking it more modest and better, silently to scorn the ignorance of a mistaken man, than by speaking to provoke the fury of a senseless one. Neither did I do this without the authority of the divine teaching, since it is written, Speak not in the ears of a fool, lest when he hear you he should despise the wisdom of your words; and again, “Answer not a fool according to his folly, lest you also be like him.” And we are, moreover, bidden to keep what is holy within our own knowledge, and not expose it to be trodden down by swine and dogs, since the Lord speaks, saying, “Give not that which is holy unto the dogs, neither cast your pearls before swine, lest they trample them under their feet, and turn again and rend you.” For when you used often to come to me with the desire of contradicting rather than with the wish to learn, and preferred impudently to insist on your own views, which you shouted with noisy words, to patiently listening to mine, it seethed to me foolish to contend with you; since it would he an easier and slighter thing to restrain the angry waves of a turbulent sea with shouts, than to check your madness by arguments. Assuredly it would be both a vain and ineffectual labour to offer light to a blind man, discourse to a deaf one, or wisdom to a brute; since neither can a brute apprehend, nor can a blind man admit the light, nor can a deaf man hear.
Source: The Treatises of Cyprian (New Advent)