John of Damascus: Exposition of the Orthodox Faith 48Concerning the manner of the Mutual Communication.

Now we have often said already that essence is one thing and subsistence another, and that essence signifies the common and general form of subsistences of the same kind, such as God, man, while subsistence marks the individual, that is to say, Father, Son, Holy Spirit, or Peter, Paul. Observe, then, that the names, divinity and humanity, denote essences or natures: while the names, God and man, are applied both in connection with natures, as when we say that God is incomprehensible essence, and that God is one, and with reference to subsistences, that which is more specific having the name of the more general applied to it, as when the Scripture says, Therefore God, thy God, hath anointed thee, or again, There was a certain man in the land of Uz, for it was only to Job that reference was made.

Therefore, in the case of our Lord Jesus Christ, seeing that we recognise that He has two natures but only one subsistence compounded of both, when we contemplate His natures we speak of His divinity and His humanity, but when we contemplate the subsistence compounded of the natures we sometimes use terms that have reference to His double nature, as "Christ," and "at once God and man," and "God Incarnate;" and sometimes those that imply only one of His natures, as "God" alone, or "Son of God," and "man" alone, or "Son of Man;" sometimes using names that imply His loftiness and sometimes those that imply His lowliness. For He Who is alike God and man is one, being the former from the Father ever without cause, but having become the latter afterwards for His love towards man.

When, then, we speak of His divinity we do not ascribe to it the properties of humanity. For we do not say that His divinity is subject to passion or created. Nor, again, do we predicate of His flesh or of His humanity the properties of divinity: for we do not say that His flesh or His humanity is uncreated. But when we speak of His subsistence, whether we give it a name implying both natures, or one that refers to only one of them, we still attribute to it the properties of both natures. For Christ, which name implies both natures, is spoken of as at once God and man, created and uncreated, subject to suffering and incapable of suffering: and when He is named Son of God and God, in reference to only one of His natures, He still keeps the properties of the co-existing nature, that is, the flesh, being spoken of as God who suffers, and as the Lord of Glory crucified, not in respect of His being God but in respect of His being at the same time man. Likewise also when He is called Man and Son of Man, He still keeps the properties and glories of the divine nature, a child before the ages, and man who knew no beginning; it is not, however, as child or man but as God that He is before the ages, and became a child in the end. And this is the manner of the mutual communication, either nature giving in exchange to the other its own properties through the identity of the subsistence and the interpenetration of the parts with one another. Accordingly we can say of Christ: This our God was seen upon the earth and lived amongst men, and This man is uncreated and impossible and uncircumscribed.