Confession of one Christ from two natures
Cyril opens his letter to the emperor by confessing the orthodox faith about Christ, then answers an anticipated objection.
We confess, then, that the only-begotten Son of God is perfect God, consubstantial with the Father in divinity and consubstantial with us in humanity. A union of natures has occurred, and from this we confess one Christ, one Son, one Lord. If it seems good, let us take as an example the composition by which we ourselves are human. We are composed of soul and body, and we see two natures, one of the body and another of the soul, yet the one human being from both in union does not make us think of two human beings because he is composed from two natures, but one human being. For if we do away with the fact that the one and only Christ is from two different natures, our opponents will say: if the whole is one nature, how did he become human, or what flesh did he take to himself? As for those who say that a mixture or confusion or blending of God the Word with the flesh occurred, the catholic and apostolic church anathematizes them.
Greek
Τοιγαροῦν ὁμολογοῦμεν τὸν μονογενῆ υἱὸν τοῦ θεοῦ θεὸν τέλειον, ὁμοούσιον τῷ πατρὶ κατὰ τὴν θεότητα καὶ ὁμοούσιον ἡμῖν τὸν αὐτὸν κατὰ τὴν ἀνθρωπότητα. ∆ύο γὰρ φύσεων ἕνωσις γέγονεν, ὅθεν ἕνα Χριστόν, ἕνα υἱόν, ἕνα κύριον ὁμολογοῦμεν. Καὶ εἰ δοκεῖ, δειξώμεθα εἰς παράδειγμα τὴν καθ' ἡμᾶς αὐτοὺς σύνθεσιν καθ' ἣν ἐσμὲν ἄνθρωποι. Συντεθείμεθα γὰρ ἐκ ψυχῆς καὶ σώματος καὶ ὁρῶμεν φύσεις δύο, ἑτέραν μὲν τοῦ σώματος, ἑτέραν δὲ τῆς ψυχῆς, ἀλλ' εἷς ἐξ ἀμφοῖν καθ' ἕνωσιν ἄνθρωπος καὶ οὐχὶ τὸ ἐκ δύο φύσεων συντεθεῖσθαι δύο ἀνθρώπους τὸν ἕνα νοεῖσθαι παρασκευάζει, ἀλλ' ἕνα ἄνθρωπον. Ἐὰν γὰρ ἀνέλωμεν τὸ ὅτι ἐκ δύο καὶ διαφόρων φύσεων ὁ εἷς καὶ μόνος ἐστὶ Χριστός, ἐροῦσιν οἱ δι' ἐναντίας· εἰ μία φύσις τὸ ὅλον, πῶς ἐνηνθρώπησεν ἢ ποίαν δὲ ἀνεποιήσατο σάρκα; Τοὺς δὲ λέγοντας ὅτι κρᾶσις ἢ σύγχυσις ἢ φυρμὸς ἐγένετο τοῦ θεοῦ λόγου πρὸς τὴν σάρκα, τούτους ἀναθεματίζει ἡ καθολικὴ καὶ ἀποστολικὴ ἐκκλησία.