It was the center of the revelation to Israel that the Lord is a ferociously jealous God, that he brooks no almost-gods, no “next” powers “after” the Father of all. “Hear, O Israel, the Lord your God is one God,” is the first creed of the church also. In the Bible there is the Lord, the Creator of all things, and there are his creatures, and there is nothing in between; there is no ontological overlap, no pantheon of not-quite-gods or divine creatures.
So which is the Logos, Creator or creature? For such Bible-readers as were the ancient churchmen, the question could not be ignored, but it could be long suppressed. Until finally poor Arius pressed it so urgently that it had to be faced, whereupon the church blew apart.
The outcome is familiar. A few thinkers took up Arius’s challenge and faced the church with the stark alternative: either stop worshiping the Son, because he is a creature and Christians do not worship creatures, or acknowledge that the Son is Creator, God Almighty. For a time such radicals were a minority, yet with this stern biblical reasoning they eventually bullied the church, kicking and screaming, into the confession of Nicaea and Constantinople, that the Son who is from God is nevertheless, or rather just so, himself true God, that in the case of this God, being from God is not incompatible with being 100 percent God.
The thought was achieved that has since enabled all specifically Christian thought on any given subject: that to be God the Father is first to be the Father of the Son, and just and only so to be God; that to be God the Son is first to be the Son of this Father, and just and only so to be God, and that to be God the Spirit is first to be the Spirit of this Father resting on this Son, and just and only so to be God; so that only in their mutuality is there God at all. God—if I may use my own jargon—is what happens between Jesus and the one he called Father, as they are freed for each other by their Spirit.
So Jesus is the Son, who is of one being with the Father, either of whom can be called Lord and neither of whom can be called the Lord without the other. From A.D. 381 on that has been the dogma of the holy catholic church.
(Robert W. Jenson, “With No Qualifications: The Christological Maximalism of the Christian East,” in Ancient & Postmodern Christianity, pp. 16-17)