17 Lo, if dogs— for a case must be imagined, in order that things may be seen more clearly— if dogs, I say, and asses, and along with them water-wagtails, if the twittering swallows, and pigs also, having acquired some of the feelings of men, were to think and suppose that you were gods, and to propose to offer sacrifices in your honour, not of other things and substances, but of those with which they are wont to be nourished and supported, according to their natural inclination—we ask you to say whether you would consider this an honour, or rather a most outrageous affront, when the swallows slew and consecrated flies to you, the water-wagtails ants; when the asses put hay upon your altars, and poured out libations of chaff; when the dogs placed bones, and burned human excrements at your shrines; when, lastly, the pigs poured out before you a horrid mess, taken from their frightful hog-pools and filthy maws?
Would you not in this case, then, be inflamed with rage that your greatness was treated with contumely, and account it an atrocious wrong that you were greeted with filth? But, you reply, you honour the gods with the carcasses of bulls, and by slaying other living creatures. And in what respect does this differ from that, since these sacrifices, also, if they are not yet, will nevertheless soon be, dung, and will become rotten after a very short time has passed? Finally, cease to place fire upon your altars, then indeed you will see that consecrated flesh of bulls, with which you magnify the honour of the gods, swelling and heaving with worms, tainting and corrupting the atmosphere, and infecting the neighbouring districts with unwholesome smells.
Now, if the gods were to enjoin you to turn these things to your own account, to make your meals from them in the usual way; you would flee to a distance, and, execrating the smell, would beg pardon from the gods, and bind yourselves by oath never again to offer such sacrifices to them. Is not this conduct of yours mockery, then? Is it not to confess, to make known that you do not know what a deity is, nor to what power the meaning and title of this name should be given and applied?
Do you give new dignity to the gods by new kinds of food? Do you honour them with savours and juices, and because those things which nourish you are pleasing and grateful to you? Do you believe that the gods also flock up to enjoy their pleasant taste, and, just as barking dogs, lay aside their fierceness for mouthfuls, and pretty often fawn upon those who hold these out?
Source: Against the Heathen (New Advent)