Apollinaris, affecting to agree with the Church as to the unity of the Trinity, though not this even with entire soundness of belief, as to the Incarnation of the Lord, blasphemes openly. For he says that the flesh of our Saviour was either altogether devoid of a human soul, or, at all events, was devoid of a rational soul. Moreover, he says that this same flesh of the Lord was not received from the flesh of the holy Virgin Mary, but came down from heaven into the Virgin; and, ever wavering and undecided, he preaches one while that it was co-eternal with God the Word, another that it was made of the divine nature of the Word. For, denying that there are two substances in Christ, one divine, the other human, one from the Father, the other from his mother, he holds that the very nature of the Word was divided, as though one part of it remained in God, the other was converted into flesh: so that whereas the truth says that of two substances there is one Christ, he affirms, contrary to the truth, that of the one divinity of Christ there have become two substances. This, then, is the doctrine of Apollinaris.
Nestorius, whose disease is of an opposite kind, while pretending that he holds two distinct substances in Christ, brings in of a sudden two Persons, and with unheard of wickedness would have two sons of God, two Christs,— one, God, the other, man, one, begotten of his Father, the other, born of his mother. For which reason he maintains that Saint Mary ought to be called, not Theotokos (the mother of God), but Christotokos (the mother of Christ), seeing that she gave birth not to the Christ who is God, but to the Christ who is man. But if any one supposes that in his writings he speaks of one Christ, and preaches one Person of Christ, let him not lightly credit it. For either this is a crafty device, that by means of good he may the more easily persuade evil, according to that of the apostle, That which is good was made death to me, Rom. 7:13 — either, I say, he craftily affects in some places in his writings to believe one Christ and one Person of Christ, or else he says that after the Virgin had brought forth, the two Persons were united into one Christ, though at the time of her conception or parturition, and for some short time afterwards, there were two Christs; so that forsooth, though Christ was born at first an ordinary man and nothing more, and not as yet associated in unity of Person with the Word of God, yet afterwards the Person of the Word assuming descended upon Him; and though now the Person assumed remains in the glory of God, yet once there would seem to have been no difference between Him and all other men. (Commonitory 12.34-35)
In these ways then do these rabid dogs, Nestorius, [and] Apollinaris… bark against the Catholic faith: Photinus, by denying the Trinity; Apollinaris, by teaching that the nature of the Word is mutable, and refusing to acknowledge that there are two substances in Christ, denying moreover either that Christ had a soul at all, or, at all events, that he had a rational soul, and asserting that the Word of God supplied the place of the rational soul; Nestorius, by affirming that there were always or at any rate that once there were two Christs. But the Catholic Church, holding the right faith both concerning God and concerning our Saviour, is guilty of blasphemy neither in the mystery of the Trinity, nor in that of the Incarnation of Christ. For she worships both one Godhead in the plenitude of the Trinity, and the equality of the Trinity in one and the same majesty, and she confesses one Christ Jesus, not two; the same both God and man, the one as truly as the other. One Person indeed she believes in Him, but two substances; two substances but one Person: Two substances, because the Word of God is not mutable, so as to be convertible into flesh; one Person, lest by acknowledging two sons she should seem to worship not a Trinity, but a Quaternity.
In God there is one substance, but three Persons; in Christ two substances, but one Person. In the Trinity, another and another Person, not another and another substance (distinct Persons, not distinct substances); in the Saviour another and another substance, not another and another Person, (distinct substances, not distinct Persons). How in the Trinity another and another Person (distinct Persons) not another and another substance (distinct substances)? Because there is one Person of the Father, another of the Son, another of the Holy Ghost; but yet there is not another and another nature (distinct natures) but one and the same nature. How in the Saviour another and another substance, not another and another Person (two distinct substances, not two distinct Persons)? Because there is one substance of the Godhead, another of the manhood. But yet the Godhead and the manhood are not another and another Person (two distinct Persons), but one and the same Christ, one and the same Son of God, and one and the same Person of one and the same Christ and Son of God, in like manner as in man the flesh is one thing and the soul another, but one and the same man, both soul and flesh. In Peter and Paul the soul is one thing, the flesh another; yet there are not two Peters,— one soul, the other flesh, or two Pauls, one soul, the other flesh—but one and the same Peter, and one and the same Paul, consisting each of two diverse natures, soul and body. Thus, then, in one and the same Christ there are two substances, one divine, the other human; one of (ex) God the Father, the other of (ex) the Virgin Mother; one co-eternal with and co-equal with the Father, the other temporal and inferior to the Father; one consubstantial with his Father, the other, consubstantial with his Mother, but one and the same Christ in both substances. There is not, therefore, one Christ God, the other man, not one uncreated, the other created; not one impassible, the other passible; not one equal to the Father, the other inferior to the Father; not one of his Father (ex), the other of his Mother (ex), but one and the same Christ, God and man, the same uncreated and created, the same unchangeable and incapable of suffering, the same acquainted by experience with both change and suffering, the same equal to the Father and inferior to the Father, the same begotten of the Father before time, (before the world), the same born of his mother in time (in the world), perfect God, perfect Man. In God supreme divinity, in man perfect humanity. Perfect humanity, I say, forasmuch as it has both soul and flesh; the flesh, very flesh; our flesh, his mother’s flesh; the soul, intellectual, endowed with mind and reason. There is then in Christ the Word, the soul, the flesh; but the whole is one Christ, one Son of God, and one our Saviour and Redeemer: One, not by I know not what corruptible confusion of Godhead and manhood, but by a certain entire and singular unity of Person. For the conjunction has not converted and changed the one nature into the other, (which is the characteristic error of the Arians), but rather has in such wise compacted both into one, that while there always remains in Christ the singularity of one and the self-same Person, there abides eternally withal the characteristic property of each nature; whence it follows, that neither does God (i.e., the divine nature) ever begin to be body, nor does the body ever cease to be body. The which may be illustrated in human nature: for not only in the present life, but in the future also, each individual man will consist of soul and body; nor will his body ever be converted into soul, or his soul into body; but while each individual man will live for ever, the distinction between the two substances will continue in each individual man for ever. So likewise in Christ each substance will for ever retain its own characteristic property, yet without prejudice to the unity of Person. (ibid. 13.36-37)
Accursed be Apollinaris, who affirms that the Godhead of Christ is marred by conversion, and defrauds Him of the property of perfect humanity.
Accursed be Nestorius, who denies that God was born of the Virgin, affirms two Christs, and rejecting the belief of the Trinity, brings in a Quaternity.
But blessed be the Catholic Church, which worships one God in the completeness of the Trinity, and at the same time adores the equality of the Trinity in the unity of the Godhead, so that neither the singularity of substance confounds the propriety of the Persons, not the distinction of the Persons in the Trinity separates the unity of the Godhead.
Blessed, I say, be the Church, which believes that in Christ there are two true and perfect substances but one Person, so that neither does the distinction of natures divide the unity of Person, nor the unity of Person confound the distinction of substances.
Blessed, I say, be the Church, which understands God to have become Man, not by conversion of nature, but by reason of a Person, but of a Person not feigned and transient, but substantial and permanent.
Blessed, I say, be the Church, which declares this unity of Person to be so real and effectual, that because of it, in a marvellous and ineffable mystery, she ascribes divine attributes to man, and human to God; because of it, on the one hand, she does not deny that Man, as God, came down from heaven, on the other, she believes that God, as Man, was created, suffered, and was crucified on earth; because of it, finally, she confesses Man the Son of God, and God the Son of the Virgin.
Blessed, then, and venerable, blessed and most sacred, and altogether worthy to be compared with those celestial praises of the Angelic Host, be the confession which ascribes glory to the one Lord God with a threefold ascription of holiness. For this reason moreover she insists emphatically upon the oneness of the Person of Christ, that she may not go beyond the mystery of the Trinity (that is by making in effect a Quaternity.) (ibid. 16.41)