11 The Son draws His life from that Father Who truly has life; the Only begotten from the Unbegotten, Offspring from Parent, Living from Living. As the Father has life in Himself, even so gave He to the Son also to have life in Himself. The Son is perfect from Him that is perfect, for He is whole from Him that is whole. This is no division or severance, for Each is in the Other, and the fullness of the Godhead is in the Son. Incomprehensible is begotten of Incomprehensible, for none else knows Them, but Each knows the Other; Invisible is begotten of Invisible, for the Son is the Image of the invisible God, and he that has seen the Son has seen the Father also.
There is a distinction, for They are Father and Son; not that Their Divinity is different in kind, for Both are One, God of God, One God Only begotten of One God Unbegotten. They are not two Gods, but One of One; not two Unbegotten, for the Son is born of the Unborn. There is no diversity, for the life of the living God is in the living Christ. So much I have resolved to say concerning the nature of their Divinity; not imagining that I have succeeded in making a summary of the faith, but recognising that the theme is inexhaustible. So faith, you object, has no service to render, since there is nothing that it can comprehend. Not so; the proper service of faith is to grasp and confess the truth that it is incompetent to comprehend its Object.
Source: On the Trinity (New Advent)