After this, Celsus next asserts that “Those herdsmen and shepherds who followed Moses as their leader, had their minds deluded by vulgar deceits, and so supposed that there was one God.” Let him show, then, how, after this irrational departure, as he regards it, of the herdsmen and shepherds from the worship of many gods, he himself is able to establish the multiplicity of deities that are found among the Greeks, or among those other nations that are called Barbarian. Let him establish, therefore, the existence of Mnemosyne, the mother of the Muses by Zeus; or of Themis, the parent of the Hours; or let him prove that the ever naked Graces can have a real, substantial existence.
But he will not be able to show, from any actions of theirs, that these fictitious representations of the Greeks, which have the appearance of being invested with bodies, are (really) gods. And why should the fables of the Greeks regarding the gods be true, any more than those of the Egyptians for example, who in their language know nothing of a Mnemosyne, mother of the nine Muses; nor of a Themis, parent of the Hours; nor of a Euphrosyne, one of the Graces; nor of any other of these names?
How much more manifest (and how much better than all these inventions!) is it that, convinced by what we see, in the admirable order of the world, we should worship the Maker of it as the one Author of one effect, and which, as being wholly in harmony with itself, cannot on that account have been the work of many makers; and that we should believe that the whole heaven is not held together by the movements of many souls, for one is enough, which bears the whole of the non-wandering sphere from east to west, and embraces within it all things which the world requires, and which are not self-existing!
For all are parts of the world, while God is no part of the whole. But God cannot be imperfect, as a part is imperfect. And perhaps profounder consideration will show, that as God is not a part, so neither is He properly the whole, since the whole is composed of parts; and reason will not allow us to believe that the God who is over all is composed of parts, each one of which cannot do what all the other parts can.
Source: Against Celsus (New Advent)