By Water & Blood

Chapter 2: That the grace of Christ granted the Church a special knowledge of Father and Son

To confess one God, in distinction from the polytheistic error of the Greeks, was something the children of the Jews received first. But to know the same God also as Father of an only-begotten Son is a singular privilege which saving grace has bestowed upon the Church. And she knows Jesus Christ alone as Son, and no other—not according to the birth of the flesh which he assumed (for this she has been taught to call the form of a servant and the Son of Man), but according to that birth from God the Father himself before all ages which is unknown to all. By this birth the fullness of the Father’s Godhead caused the Son himself also to subsist as God (ὑπεστήσατο): not as one possessing a Godhead of his own, separated off from the Father, nor one without beginning and unbegotten, nor drawing to himself from somewhere else a Godhead foreign and alien to the Father, but filled from the very participation (μετουσία) in the Father, which pours forth upon him as from a fountain. For the great Apostle taught that in him alone dwells “all the fulness of the Godhead”—that is, of the Father’s Godhead. Therefore one God is proclaimed by the Church of God, “and there is none other but he”; and one also is the only-begotten Son of God, the image of the Father’s Godhead, and for this reason God.