The Divine Institutes

But let us come to the philosophers, whose authority is regarded as more certain than that of the poets. Plato asserts His monarchy, saying that there is but one God, by whom the world was prepared and completed with wonderful order. Aristotle, his disciple, admits that there is one mind which presides over the world. Antisthenes says that there is one who is God by nature, the governor of the whole system. It would be a long task to recount the statements which have been made respecting the Supreme God, either by Thales, or by Pythagoras and Anaximenes before him, or afterwards by the Stoics Cleanthes and Chrysippus and Zeno, or of our countrymen, by Seneca following the Stoics, and by Tullius himself, since all these attempted to define the being of God, and affirmed that the world is ruled by Him alone, and that He is not subject to any nature, since all nature derives its origin from Him.

Hermes, who, on account of his virtue and his knowledge of many arts, deserved the name of Trismegistus, who preceded the philosophers in the antiquity of his doctrine, and who is reverenced by the Egyptians as a god, in asserting the majesty of the one God with infinite praises, calls Him Lord and Father, and says that He is without a name because He does not stand in need of a proper name, inasmuch as He is alone, and that He has no parents, since He exists of Himself and by Himself. In writing to his son he thus begins: To understand God is difficult, to describe Him in speech is impossible, even for one to whom it is possible to understand Him; for the perfect cannot be comprehended by the imperfect, nor the invisible by the visible.