"we have beheld his glory"

"Because the reality of the relation is only maintained on the created side, the Incarnation cannot be reduced to an episode in the longer (eternal) life of the Logos.  Rather, the episode of this life must express fully the whole immutable reality on which it depends:  the person of the eternal Son.  What the Logos thus receives ex Maria, he receives in a mode that, rather than changing him, recapitulates [(read as something like transfigures, divinizes)] the reality into which he is incarnated" (166), such that (to quote Gregory of Nyssa) "'the mortal [element] that came to be in the immortal became immortality, and the corruptible [was] likewise changed into incorruptibility, and all the other [properties] similarly were transformed into impassible and divine [properties]. . . .'"

     Aaron Riches on St. Thomas Aquinas on the Incarnation, quoting also Gregory of Nyssa, Ad Theophilum (GNO 3.1, pp. 124-125), as trans. Behr, in Ecce homo:  on the divine unity of Christ, Interventions (Grand Rapids, MI:  Eerdmans, 2016), 166, 167, underscoring mine.  This in the context of Aquinas' famous insistence (a highly technical one) that God is not "really" related to the universe:

'the union of which we are speaking is not really in God, except only in our way of thinking; but in the human nature, which is a creature, it is really' [(165, quoting ST III.2.7)]. 

The relation between God and created being, the unity of this human nature with the Logos, allows God himself to be the foundation of reality on the creaturely side, while on the side of God—precisely because his is this foundation of reality—the relation cannot alter him in any way [(168)].