In 451 A.D., an ecumenical council was convened in Chalcedon, located in Asia Minor. They assembled to deliberate on the Bible’s teaching concerning the Person of Jesus Christ. Their conclusion is expressed in the Definition of Chalcedon, which upheld the conclusions reached two decades earlier in Ephesus (431 A.D.), i.e., Christ is not two persons but one, against the Nestorians. Chalcedon further taught that the union of the two natures in the one Person of Christ did not annul those two natures; rather, they maintain their own distinct properties. This refuted the claims of the Eutychians, who held that Christ’s divine and human natures were combined to form one, new nature.
Therefore, following the holy fathers, we all with one accord teach men to acknowledge one and the same Son, our Lord Jesus Christ, at once complete in Godhead and complete in manhood, truly God and truly man, consisting also of a reasonable soul and body; of one substance with the Father as regards his Godhead, and at the same time of one substance with us as regards his manhood; like us in all respects, apart from sin; as regards his Godhead, begotten of the Father before the ages, but yet as regards his manhood begotten, for us men and for our salvation, of Mary the Virgin, the God-bearer; one and the same Christ, Son, Lord, Only-begotten, recognized in two natures, without confusion, without change, without division, without separation; the distinction of natures being in no way annulled by the union, but rather the characteristics of each nature being preserved and coming together to form one person and subsistence, not as parted or separated into two persons, but one and the same Son and Only-begotten God the Word, Lord Jesus Christ; even as the prophets from earliest times spoke of him, and our Lord Jesus Christ himself taught us, and the creed of the fathers has handed down to us.