19 The gods dwell in images— each wholly in one, or divided into parts, and into members? For neither is it possible that there can be at one time one god in several images, nor, again, divided into parts by his being cut up. For let us suppose that there are ten thousand images of Vulcan in the whole world: is it possible at all, as I said, that at one time one deity can be in all the ten thousand? I do not think so. Do you ask wherefore?
Because things which are naturally single and unique, cannot become many while the integrity of their simplicity is maintained. And this they are further unable to become if the gods have the forms of men, as your belief declares; for either a hand separated from the head, or a foot divided from the body, cannot manifest the perfection of the whole, or it must be said that parts can be the same as the whole, while the whole cannot exist unless it has been made by gathering together its parts.
Moreover, if the same deity shall be said to be in all the statues, all reasonableness and soundness is lost to the truth, if this is assumed that at one tithe one can remain in them all; or each of the gods must be said to divide himself from himself, so that he is both himself and another, not separated by any distinction, but himself the same as another. But as nature rejects and spurns and scorns this, it must either be said and confessed that there are Vulcans without number, if we decide that he exists and is in all the images; or he will be in none, because he is prevented by nature from being divided among several.
Source: Against the Heathen (New Advent)