9 We worship the gods, you say, by means of images. What then? Without these, do the gods not know that they are worshipped, and will they not think that any honour is shown to them by you? Through bypaths, as it were, then, and by assignments to a third party, as they are called, they receive and accept your services; and before those to whom that service is owed experience it, you first sacrifice to images, and transmit, as it were, some remnants to them at the pleasure of others. And what greater wrong, disgrace, hardship, can be inflicted than to acknowledge one god, and yet make supplication to something else— to hope for help from a deity, and pray to an image without feeling? Is not this, I pray you, that which is said in the common proverbs: “to cut down the smith when you strike at the fuller;” “and when you seek a man's advice, to require of asses and pigs their opinions as to what should be done?”
Source: Against the Heathen (New Advent)