The Council of Chalcedon (451) met to resolve the Monophysite controversy (a heresy saying Christ had one nature) in which the Eutychians refused to confess the existence of two nature in Christ. It summarizes the Church’s teaching on the natures of Christ in negative terms.
This Council asked, “in what sense was Jesus truly man,” and “how was He both God and man?” Many answers have been given: Apollinarianism destroyed Christ’s true manhood by saying He did not have a “rational soul.” Nestorianism destroyed the unity of His person by radically separating His divine nature from His human nature and making two Christ’s. Eutychianism destroyed the distinction of the two natures by teaching that Christ’s human nature was absorbed into His divine nature.
In the Belgic Confession of Faith, Article 9, the Reformed churches confess that “we do willingly receive the three creeds, namely, that of the Apostles’, of Nicea, and of Athanasius; likewise that which, conformable thereunto, is agreed upon by the ancient fathers.” The Definition of Chalcedon is appended to this book of creeds and confessions at it explains who is the Jesus Christ of the three great ecumenical creeds.
HT: Christian Creeds and Confessions Pocket Edition, 12.
We, then, following the holy Fathers, all with one consent,
teach men to confess one and the same Son, our Lord Jesus Christ:
the same perfect in deity
and also perfect in humanity;
truly God and truly man, of a rational soul and body;
consubstantial with the Father concerning His divine nature,
and consubstantial with us according to His human nature;
in all things like unto us, but without sin;
begotten before all ages of the Father
concerning His divine nature,
and in these latter days, for us and for our salvation,
born of the Virgin Mary,
the Mother of God (1), concerning His human nature;
One and the same Christ, Son, Lord, Only begotten,
to be acknowledged in two natures,
unconfusedly, unchangeably, indivisibly, inseparably;
the distinction of natures being by no means taken away by the union,
but rather the property of each nature being preserved,
and concurring in one Person and one Subsistence,
not parted or divided into two persons,
but one and the same Son, and only begotten,
God the Word,
the Lord Jesus Christ;
As the prophets from the beginning have declared concerning Him,
and the Lord Jesus Christ Himself has taught us,
and the Creed of the holy Fathers has handed down to us.
(1) The title “mother of God” (Greek, theotokos) was used to express that Jesus derived a true human nature from Mary, and that the son of Mary was God from the moment of His conception, that is, He did not become God at a later date.