My two favorite paragraphs from Jenson’s Triune Identity :

“‘Out of the being of the Father’ affirms just that origin of Christ within God’s own self which Arius most feared. The phrase says that the Son is not an entity originated outside God by God’s externally directed choice, that he is not in any sense a creature. And it says that there is differentiation within God, that the relation to the Son is an ‘internal relation’ in the Father, a relation necessary to his being God the Father. To be God is to be related . With that the fathers contradicted the main principle of Hellenic theology.

“‘Begotten and not created’ makes exactly that distinction between two ways of being originated from God, the lack of which enabled the subordinationist glissando from God himself, who is unoriginated, to us, who are originated, through the Son, who is a bit of each. On the contrary, we are ‘created,’ the Son is ‘begotten,’ and these are just two different things. Nobody claimed to know exactly what ‘begotten’ meant in this connection, and yet a tremendous assertion is made: there is a way of being begun , of receiving one’s being, which is proper to Godhead itself. To be God is not only to give being, it is also to receive being. And there went the rest of Plato.”

One gloss: Jenson’s focus on the issue of the Son’s begottenness has received a sophisticated and thorough elaboration in Lewis Ayres’s recent book on Nicaea and Its Legacy . Debates about the divine begetting are at the heart of the Arian controversy, Ayres shows.