“the Son is in the Father . . . because the whole being of the Son is proper to the Father’s ousia, as radiance from light and a stream from a fountain; so that whosoever sees the Son, sees what is proper to the Father and knows that the Son’s being, as from the Father, is the Father and is therefore in the Father. For the Father is in the Son, since the Son is what is from the Father and proper to him, as there is in the radiance the sun, and in the word the thought, and in the stream the fountain: for whoso thus contemplates the Son, contemplates what is proper to the Father’s ousia, and knows that the Father is in the Son.
Leithart quotes Athanasius, and finds the nugget phrase: “in the word, the thought”. Now that’s full, but you can’t draw a mental picture of it. If you came to this passage looking for a more clear spatial metaphor for your Trinity category, you didn’t get it.
When the Fathers are doing this thing, this attempt to exegete theology, they are not doing what we’ve been doing since the Scholastics, and doing feverishly since the Enlightenment. They are not trying to draw a diagram. What they are doing is poetry — but not what “poetry” means to you.
Not “poetry” in the sense of “expression of feeling as opposed to thought” or “escape from rationality into mysticism” (yuck.) These are modern dichotomies. These are post-line-of-despair categories (cf Frances Scheaffer).
They are doing poetry the way David Hart fills out the word “rhetoric”…RATIONALITY THAT IS SO FULL AND GLORIOUS IT MUST SPILL OVER THE STRUCTURES OF PROSE. So the theological work is not intended to give you a diagram, but it is meant to help you understand it better, by giving you the same truth in a different language.
If you know the English word for “tree”, and the elvish word for “tree”, you are able to see the tree better. The two words are not the same nominal sign, they are two signs to the one thing. So, poetry is not translatable into prose, and theology is not translatable into diagrams. This does not mean theology is not true — least of all does it mean theology is directed at “faith” instead of at “reason” (yuck.) — but that theology is directed at the synthetic faculty, as opposed to the analytical faculty. God is bigger than your mind, so to talk of Him we must rhapsodize, so that He is not falsified to your intellect.