Sect. 172The Word Incarnate as One Physical Person, According to the Doctrine of the Church Against NestoriusThe Word Incarnate as One Physical Person, According to the Doctrine of the Church Against Nestorius

I. After the Church had defined the consubstantiality of the Logos with the Eternal Father against the Arians, and His consubstantiality with man against the Apollinarists, Nestorius arose to impugn the nature of the union of the Divine Logos with human nature. In his opinion, the two dogmas, that Christ is really God and really man, could only be upheld if in Christ there were two persons, one Divine, the other human, but neither of them God and man at the same time. Between these two persons he divided the Divine and human attributes of Christ The identity of the Son of God with the Son of Mary, set forth in the Apostles’ Creed and generally in the teaching of the Church, was reduced by Nestorius to a moral union: the Son of God dwelling in the Son of Mary as in His temple; Jesus not being God, but only a God-bearing man (ἄνθρωπος θεοφόρος), participating to a certain degree in the dignity, authority, and power of the Logos, and being designated by the same names as the Logos, provided these did not expressly signify the physical essence of the Logos. Thus Jesus was not to be called Logos, nor vice versâ, but both might be termed Christ, Son of God, Lord, and even God (in the sense in which Moses was the God of Pharaoh). The disciples of Nestorius compared the union of the Logos with Jesus to the union between husband and wife, which makes them two in one flesh.

II. St. Cyril of Alexandria, whose doctrine was accepted by the Council of Ephesus, formulated the Catholic dogma against Nestorius. He found the duality of persons sufficiently refuted in the Symbols of the Apostles and of Nicæa, which attribute to “one subject” the eternal birth from the Father and the temporal birth from the Virgin, thus establishing the unity of Person and precluding the possibility of predicating the human and Divine attributes of two distinct subjects. See the second Epist. of St. Cyril to Nestorius, and the Anathematisms of the Fifth General Council, can. 2, 3, 6.

1. If the Logos and the human substance are really one subject, the union of the two substances is necessarily more than moral, relative, or accidental: it must be conceived as a true composition, resulting in one indivisible Being, and involving a true appropriation of the human substance by the Person of the Logos, and, as a consequence, the loss of independence or personality in the human substance. This substantial union was expressed in the formula, ἕνωσις καθʼ ὑπόστασιν, secundum substantiam; but this term had not then the classical and well-defined meaning which it afterwards acquired: it did not exclude the unity of nature, as clearly appears from the expressions used as its equivalents, e.g. ἕνωσις κατὰ φύσιν (unio secundum naturam), etc. On the other hand, the formula ἕνωσις φυσική) did not then imply a “unity of nature” in the sense which later on became classical, for it was used in dogmatic definitions against the Monophysites and Monothelites. The tendency of both these formulas was merely to affirm a substantial union against the moral union upheld by Nestorius; they did not claim to define exactly the specific difference of this union from all other substantial unions. That difference was pointed out by describing the union as admirable, ineffable, and incomprehensible. St. Cyril avoided the analogical illustrations, so frequent among earlier Fathers, of κρᾶσις and συμφυία (mixture, concretion), on account of Nestorian misinterpretation; he preferred more abstract expressions, but he constantly illustrated them by the analogy of the union of the flesh with the rational soul in man; an illustration also used by St. Augustine, and now become classical.

2. In the union of body and soul we have, as in the union of the Logos with “the flesh”: (1) A true, substantial, physical, and metaphysical union of a higher with a lower substance, resulting in one total substance, in consequence of the infusion or ingrafting of the higher in the lower. (2) The distinction of the two substances remains intact after the union: the soul retains its own spiritual life, and is not affected in its essence by the passions of the body; the body also retains its properties, although the union raises it to a much higher perfection. (3) The lower substance is subordinated to and dependent on the higher in both the physical and ethical order. (4) The union is based entirely on the power of the higher element; it consists in this, that the soul holds, possesses, and rules the corporeal element as its own. This analogy had the advantage of reducing to their exact signification the analogies misused by Nestorius. The humanity of Christ is indeed the temple and the throne of the Divinity, but the temple and throne appertain to and are connected with the Divinity after the manner in which the human body appertains to and is connected with the informing soul. Again, the humanity of Christ is the organ and instrument by which the Logos operates, but it is “His” organ, as much as the members of the body are the organs by which the soul operates. Lastly, the humanity of Christ is an image and a vesture of the Logos, not, however, distinct and separate from Him, but united as our body is to the soul.

As special effect, and therefore as a manifest sign of the substantial and physical union, St. Cyril points out that through it the flesh of Christ becomes itself a life-giving flesh, the Bread of life, the source of all the marvellous operations of the Holy Eucharist. This Sacrament, if the doctrine of Nestorius were true, would be degraded to an act of anthropophagy, the communicant receiving the flesh of man and not the flesh of God. But the substantial union of the Logos with the flesh not only endows this latter with an immanent principle of a most perfect life, but also with the power to diffuse light and life around it. When creatures not physically united with God, e.g. the saints and sacraments, are made the vehicle of supernatural life, they do not possess the life-giving power in themselves; in Christ, on the contrary, this power is as substantially inherent as the life-sustaining power in bread. There is, however, a difference: it is the proper nature of bread to support life; the vivifying power of the Body of Christ is not connatural to it, but is derived from its union with the Logos.

III. The proofs for the substantial union of the two natures in Christ were primarily taken from the texts of Scripture which represent the origin of Christ as the incarnation of the Logos, or as the assumption by the Logos of the form of servant, and from the texts in which human and Divine attributes are predicated of the same subject. Further, it was urged that, if the union were but moral, there would be no real incarnation, no more than if God had not assumed a true human body and soul. Again, if God is not truly man, then the man Jesus is not truly God, and the worship granted to Him and demanded for Him in Scripture is idolatry. Moreover, the purpose of the Incarnation cannot be attained except by a God-Man, for only a God-Man can be a priest of sufficient dignity and a victim of sufficient value to cancel the guilt of sin and merit grace; only by virtue of the power communicated to human nature by its substantial union with a Divine Person can be accomplished the thorough healing of the corruptibility of that nature and the infusion into it of Divine Life. The Redeemer of mankind can be no other than its Creator, because redemption is as much a Divine work as creation: God, therefore, can no more confer upon another the honour of redeeming the world than that of creating it See Petavius, lib. iii. and vi.; Thomassin, lib. iii.; Franzelin, thes. 22–25.