32 Mercury, also, has been named as though he were a kind of go-between; and because conversation passes between two speakers, and is exchanged by them, that which is expressed by this name has been produced. If this, then, is the case, Mercury is not the name of a god, but of speech and words exchanged by two persons; and in this way is blotted out and annihilated the noted Cyllenian bearer of the caduceus, born on the cold mountain top, contriver of words and names, the god who presides over markets, and over the exchange of goods and commercial intercourse.
Some of you have said that the earth is the Great Mother, because it provides all things living with food; others declare that the same earth is Ceres, because it brings forth crops of useful fruits; while some maintain that it is Vesta, because it alone in the universe is at rest, its other members being, by their constitution, ever in motion. Now if this is propounded and maintained on sure grounds, in like manner, on your interpretation, three deities have no existence: neither Ceres nor Vesta are to be reckoned in the number of the gods; nor, in fine, can the mother of the gods herself, whom Nigidius thinks to have been married to Saturn, be rightly declared a goddess, if indeed these are all names of the one earth, and it alone is signified by these titles.
Source: Against the Heathen (New Advent)