10 What wild insanity of abandoned souls! What blind audacity of reckless blasphemy! You hear of God and God; you hear of Our image. Why suggest that One is, and One is not, true God? Why distinguish between God by nature and God in name? Why, under pretext of defending the faith, do you destroy the faith? Why struggle to pervert the revelation of One God, One true God, into a denial that God is One and true? Not yet will I stifle your insane efforts with the clear words of Evangelists and Prophets, in which Father and Son appear not as one Person, but as One in nature, and Each as true God.
For the present the Law, unaided, annihilates you. Does the Law ever speak of One true God, and One not true? Does it ever speak of Either, except by the name of God, which is the true expression of Their nature? It speaks of God and God; it speaks also of God as One. Nay, it does more than so describe Them. It manifests Them as true God and true God, by the sure evidence of Their joint image. It begins by speaking of Them first by their strict name of God; then it attributes true Godhead to Both in common. For when man, Their creature, is created after the image of Both, sound reason forces the conclusion that Each of Them is true God.
Source: On the Trinity (New Advent)