The Catholic Doctrine of the Trinity and the Incarnation explained.
[36.] In these ways then do these rabid dogs, Nestorius, Apollinaris, and Photinus, 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.
[37.] But it will be well to unfold this same doctrine more distinctly and explicitly again and again.
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 hath 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 hath not converted and changed the one nature into the other, (which is the characteristic error of the Arians), but rather hath 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 doth God (i.e., the divine nature) ever begin to be body, nor doth 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.