St Gregory’s letter to Cledonius (101) has one of the most important and famous Patristic statements (present in other forms in other Fathers as well):
“Το γαρ απρόσληπτον και αθεράπευτον.”
Or, for that which is not taken up (or assumed) is not healed.
The full quotation continues,
“Ο δε ήνωται τω Θεώ, τούτο και σώζεται.
That which is united to God, that will be saved.
Εί ήμισυς έπταισεν ο ‘Αδάμ, ήμισυ και το προσειλημμένον και το σωζόμενον . Εί δε όλος, όλα τα γεννηθέντι ήνωται , και όλως σώζεται
If half of Adam fell, also half will be taken up and saved. But if all [of Adam], all of his nature will be united [to God], and all of it will be saved.
Why does this matter? Why does Christology matter? Because God has come to us to redeem, to save, to heal, the entirety of us; that gives us the power and responsibilitiy to live entirely new lives, body and soul, by the power of the Spirit, in holiness for eternal life. He has done it for us, and calls us to join him.
In positive terms, the Logos of God takes on the entirety of human nature (body, soul, spirit, mind, everything except sin) to unite it to his divine nature in his divine Person, in order to fully heal humanity.
St Gregory presents two main principles: first, that God the Logos united full humanity to himself. Second, that the purpose of doing so is to redeem humanity, for this is the only way he could redeem it.
As he addresses the heresy of Apollinarianism (i.e., that the Logos substitutes the human mind in the human nature of Jesus Christ), he says, “Do not let the men deceive themselves and others with the assertion that the Man of the Lord, as they call Him, Who is rather our Lord and God, is without human mind. For we do not sever the Man from the Godhead, but we lay down as a dogma the Unity and Identity of Person”.
As St Gregory lists Christological errors, without using labels, he refutes adoptionism (“If any assert that the Manhood was formed and afterward was clothed with the Godhead, he too is to be condemned’), Nestorianism (“If any introduce the notion of Two Sons, one of God the Father, the other of the Mother, and discredits the Unity and Identity, may he lose his part in the adoption promised to those who believe aright . . . for there are not two Sons or two Gods.”) and even docetism (“If anyone assert that His flesh came down from heaven, and is not from hence, nor of us though above us, let him be anathema.”)
St Gregory contrasts the different properties of the human nature (passible, circumscript, earthly, tangible) with the properties of the divine nature (impassible, uncircumscript, heavenly, intangible) and asserts that they are united in one Person, “that the entire humanity, fallen through sin, might be created anew.” The deity is made man, so that manhood may be deified. We worship the Crucified God who has ascended in his deified body.
A man without a mind would be a beast, but Jesus Christ has redeemed the entirety of human nature, that we might be saved. The purpose of his Christological construct is always, and very clearly (as with St Athanasius), redemption.
“But, says such an one, the Godhead took the place of the human intellect. How does this touch me? For Godhead joined to flesh alone is not man, nor to soul alone, nor to both apart from intellect, which is the most essential part of man. Keep then the whole man, and mingle Godhead therewith, that you may benefit me in my completeness . . . He needed flesh for the sake of the flesh which had incurred condemnation, and soul for the sake of our soul, so, too, He needed mind for the sake of mind, which not only fell in Adam, but was the first to be affected, as the doctors say of illnesses.”