Athanasius ( Orations Against the Arians ) writes that “God is not like us.” This is in the context of explaining how the eternal Word differs from the ephemeral words of human beings, and how the divine Word actually does what it says: “the Word of God is not, as it were, a mere enunciation.”
Yet, criticizing Arians from another angle, Athanasius insists that even among corporeal creatures there are “offspring that are not parts of the essences from which they are and are not passible and do not lessen the beings of their progenitors.” That is, the fact that the Son comes “from” the Father doesn’t make him a “part” of the Father, and doesn’t diminish the Father’s being. His example here is light: “the radiance is from the sun and belongs to is, while the being of the sun is not thereby divided or lessened.”
This can seem arbitrary: Athanasius appeals to disanalogies between God and man when it suits his polemic, and to analogies when it suits his polemic. What rescues this from arbitrariness is the fact that Athanasius grounds these reflections in the paradeigmata and eikonas of Scripture: “Scripture has placed before us such symbols and such images, so that we may understand from them, however slightly and obscurely, as much as is accessible to us.”