As then the light from the Sun which illumines the world could never be supposed, by men of sound mind, to do so without the Sun, since the Sun’s light is united to the Sun by nature; and as, if the Light were to say: I have received from the Sun the power of illumining all things, and of giving growth and strength to them by the heat that is in me, no one will be mad enough to think that the mention of the Sun is meant to separate him from what is his nature, namely the light; so piety would have us perceive that the Divine Essence of the Word is united by nature to His own Father.
~ Illud Omnia, &c. 4
This is but one more counterexample to the “Western” and “essence” hypothesis that supposes all direct talk about the divine essence uniting the persons to be an Augustinian development. Athanasius is using the same solar metaphor that will also appear in Gregory of Nyssa.