The Chalcedon Creed includes the following affirmation:
“We should confess that our Lord Jesus Christ is the one and the same Son, the same perfect in Godhead and the same perfect in manhood, truly God and truly man, the same of a rational soul and body, consubstantial [of one substance] with the Father in Godhead, and the same consubstantial with us in manhood, like us in all things except sin;. . . one and the same Christ, Son, Lord, only-begotten, made known in two natures without confusion, without change, without division, without separation, the difference [distinction] of the natures being by no means removed [annulled] because of the union, but the property of each nature being preserved and coalescing in one person [prosopon] and one hypostasis [subsistence] – not parted or divided into two persons [prosopa], but the one and the same Son, only-begotten, divine Word, the Lord Jesus Christ, . . . (J.N.D. Kelly, Early Christian Doctrine, pp. 339-340)
Comments:
1. Unity of Natures
Belief in the unity of Christ is expressed in accordance with tradition. This is done in quite simple periphrastic expressions: ‘We confess that our Lord Jesus Christ is one and the same Son. This eis kai o autos has its history early from Ignatius of Antioch to Nicene, Ephesus, etc.
2. Distinction of Natures
The Phrase “The Same perfect in Godhead, the Same perfect in manhood, truly God and truly man, the Same [consisting] of a rational soul and a body.”
Distinction does not weaken the unity: There is a stress on the one subject in Christ. “It makes a difference in fact whether I say ‘perfect God and perfect man of a rational soul and body’ (as does the Symbol of Union) or ‘one and the same perfect in Godhead and in manhood.’” (CCT 546-547)
3. Completeness and distinction of Godhead and manhood
“The one Christ, the one incarnate Son of God is truly and perfectly God and man! Motifs recur from an earlier period, the time of the struggle against Gnostics and docetists. The Arian and Apollinarian denial of the completeness of Christ’s human nature is also refuted: Christ has a rational soul and a truly human body. Nothing may be taken away from the human nature of Christ to explain his unity.”
4, Emphatic diphysitism
“Homoousios with the Father as to his Godhead, the same homoousios with us as to his manhood…” :
Any Eutychian trend towards Monophysitism is opposed.
“made know in two natures”:
“The Alexandrian were shouting mia fusis, the Antiochenes duo fuseis. Chalcedon made its choice and said: Christ is one and the same Son, Lord, only begotten, but . Christ is one in ‘two natures’.” (CCT 548)
“‘In two natures’ and not ‘from two natures’. So the unity in Christ is not to be sought in the sphere of the natures (not in natura et secundum naturam). For the natures as such remain preserved. This is still further stressed with a threefold variation: ‘without confusion…the difference of the natures having been in no wise taken away by reason of the union, but rather the properties of each being preserved’ (swzomenhs de mallon ths idiothtos ekateras fusews). Thus the nature is the unimpaired principle of the distinction in Christ.”
5. Added without emphasis: “one person (prosopon) and one hypostasis – not parted or divided into two prosopa, but the one and the same Son, Only-begotten, divine Logos, the Lord Jesus Christ.”
Reference
CCC – Aloys Grillmeier, Christ in the Christian Tradition (John Knox Press 1975)