Incarnation of the Logos
The union of natures is not merely a matter of the union of persons, but rather the natures are gathered into one, ineffably and beyond reason, as God himself has known.
We do not say that there is a confusion or disruption of the natures, as if the nature of the Logos were changed into that of man, or the human into that of the Logos, but rather that each nature remains within its own limit.
The union has been realized by the Logos dwelling bodily in the temple born of the virgin.
If anyone claims that the union is only of persons and completely separates the natures from each other, they stray from the straight path, as Cyril notes in his interpretation.
We see the one Christ, who is God incarnate, dying bodily for sin, so that by the sprinkling of his own blood he may wholly sanctify the Church, and remaining again impassible in his divinity.
As Cyril explains in his interpretation of the pros Hebraeous epistle, if he has perfected us by water and Spirit, then he must act both divinely and humanly at once, being the same one who exists.
It is a mystery that happened ineffably and beyond mind, that divinity and humanity were united, and though the natures are distinct, yet there is one and only Son from both.
Even if the natures were diverse and unequal to one another, and ran together into unity, there is still one and only Son from both, who is truly possessed of a rational soul and is the temple united to the Logos.
As Cyril notes, it was not a bare man, one of us, who could complete the energy of the according-to-nature life, but rather, as the most holy Paul says, it was by the grace of God that the body of the Logos, who became incarnate for us, tasted death, in order that the work of abolishing death might not be attributed to the earthly body, but rather to the Logos who is united to it and subsists alongside it.
The most holy Paul says, 'by the grace of God' (Hebrews 2:9), indicating that it was God's grace that allowed the Logos to taste death for the salvation of all.
Greek
προσώπων ἑνώσει μόνον συντιθεὶς τὴν οἰκονομίαν, συλλέγων δὲ μᾶλλον εἰς ἓν τὰς φύσεις ἀποῤῥήτως γε καὶ ὑπὲρ λόγον, ὡς αὐτὸς ἔγνω ὁ Θεός. καὶ οὐ δήπου φαμὲν ἀνάχυσιν ὥσπερ τινὰ συμβῆναι περὶ τὰς φύσεις, ὡς μεταστῆναι μὲν τὴν τοῦ Λόγου φύσιν εἰς τὴν τοῦ ἀνθρώπου τυχόν· ἀλλ' οὐδὲ αὖ τὴν ἀνθρωπίνην εἰς τὴν αὐτοῦ τοῦ Λόγου· νοουμένης δὲ μᾶλλον καὶ ὑπαρχούσης ἑκατέρας ἐν τῷ τῆς ἰδίας φύσεως ὅρῳ, πεπράχθαι φαμὲν τὴν ἕνωσιν, ἐνοικήσαντος τοῦ Λόγου σωματικῶς τῷ ἐκ παρθένου ναῷ. Καὶ μετ' ὀλίγα· Εἴ τις οὖν ἄρα λέγει μόνων προσώπων τὴν ἕνωσιν, ἀποδιιστὰς ὁλοτρόπως ἀλλήλων τὰς φύσεις, ἔξω τῆς εὐθείας φέρεται τρίβου. 422 Κυρίλλου ἐκ τῆς αὐτῆς ἑρμηνείας. Ὅρα τοίνυν καὶ ἐν δυσὶ τοῖς χιμάροις τὸν ἕνα Χριστὸν, τουτέστι Θεὸν ἐνανθρωπηκότα, καὶ ἀποθνήσκοντα μὲν σαρκικῶς ὑπὲρ ἁμαρτίας, ἵνα τῷ ῥαντισμῷ τοῦ ἰδίου αἵματος ὅλην ἁγιάσῃ τὴν Ἐκκλησίαν, μεμενηκότα δὲ πάλιν ἀπαθῆ θεϊκῶς. 24 Κυρίλλου ἐκ τῆς ἑρμηνείας τῆς πρὸς Ἑβραίους ἐπιστολῆς. Εἰ δὲ τετελείωκεν ἡμᾶς δι' ὕδατος καὶ Πνεύματος, πῶς οὐκ ἐνήργει θεϊκῶς τε ἅμα καὶ ἀνθρωπίνως ὁ αὐτὸς ὑπάρχων, καὶ ὡς ἐν ἑνὶ Θεός τε ὁμοῦ καὶ ἄνθρωπος; Κυρίλλου ἐκ τῆς ἑρμηνείας τῆς πρὸς Ἑβραίους, δευτέρου τόμου. Συνέβησαν δὲ ἀλλήλαις ἀποῤῥήτως τε καὶ ὑπὲρ νοῦν θεότης καὶ ἀνθρωπότης· καὶ διάφοροι μὲν αἱ φύσεις ὁμολογουμένως, πλὴν εἷς τε καὶ μόνος ἐξ ἀμφοῖν Υἱός. Κυρίλλου ἐκ τοῦ ὑπομνήματος τῆς πρὸς Ἑβραίους ἐπιστολῆς. Εἰ γὰρ καὶ νοοῖντο διάφοροι καὶ ἀλλήλαις ἄνισοι τῶν εἰς ἑνότητα συνδεδραμηκότων αἱ φύσεις, σαρκὸς δὴ λέγω καὶ Θεοῦ, ἀλλ' οὖν εἷς τε καὶ μόνος ἐξ ἀμφοῖν Υἱὸς, ἀληθῶς 423 ἔχοντος καὶ ἡμῖν ἀραρότως τοῦ καὶ ἐμψυχῶσθαι ψυχῇ λογικῇ τὸν ἑνωθέντα τῷ Λόγῳ ναόν. Κυρίλλου ἐκ τῆς ἑρμηνείας τῆς πρὸς ἑβραίους ἐπιστολῆς. Οὐ γὰρ ἦν ἀνθρώπου ψιλοῦ καὶ τῶν καθ' ἡμᾶς ἑνὸς, τῆς κατὰ φύσιν ζωῆς ἀποπεραίνειν δύνασθαι τὴν ἐνέργειαν, διὰ τοῦτο "χάριτι Θεοῦ" καὶ αὐτὸ τὸ σῶμα τοῦ δι' ἡμᾶς ἐνανθρωπήσαντος Λόγου, καίτοι κατὰ φύσιν ὄντος ζωῆς, ὑπὲρ τῆς ἁπάντων σωτηρίας ἐγεύσατο θανάτου, καθά φησιν αὐτὸς ὁ ἱερώτατος Παῦλος, ἵνα μὴ τοῦ γηΐνου σώματος ἔργον εἶναι νομισθείη τὸ καταργῆσαι θάνατον, αὐτοῦ δὲ δὴ μᾶλλον τοῦ ἑνωθέντος αὐτῷ καὶ παρ' αὐτὸ ἑτέρου κατὰ φύσιν ὑπάρχοντος Λόγου. 25