The Chalcedonian Creed
The Chalcedonian Creed, also called the Chalcedonian Definition, is a declaration of Christ’s dual nature (dyophysite), adopted at the Council of Chalcedon in AD 451. The council was the fourth ecumenical councils accepted by Chalcedonian churches, including Catholic, Eastern Orthodox, Lutheran, Anglican and Reformed churches, and was the first council not to be recognized by Oriental Orthodox churches. The Council of Chalcedon was summoned to consider the Christological question in light of the “one-nature” (monophysite) view of Christ proposed by Eutyches. The Council ratified the Nicene Creed adopted in 325 and that creed as amended by the First Council of Constantinople in 381. The Definition implicitly addressed a number of heretical beliefs. The reference to “co-essential with the Father” was directed at Arianism; “co-essential with us” is directed at Apollinarianism; “Two Natures unconfusedly, unchangeably” refutes Eutychianism and Monophysitism; and “indivisibly, inseparably” and “Theotokos” are against Nestorianism.
The Chalcedonian Definition:
“Following, then, the holy Fathers, we all unanimously teach that our Lord Jesus Christ is to us One and the same Son, the Self-same Perfect in Godhead, the Self-same Perfect in Manhood; truly God and truly Man; the Self-same of a rational soul and body; co-essential with the Father according to the Godhead, the Self-same co-essential with us according to the Manhood; like us in all things, sin apart; before the ages begotten of the Father as to the Godhead, but in the last days, the Self-same, for us and for our salvation (born) of Mary the Virgin Theotokos as to the Manhood; One and the Same Christ, Son, Lord, Only-begotten; acknowledged in Two Natures unconfusedly, unchangeably, indivisibly, inseparably; the difference of the Natures being in no way removed because of the Union, but rather the properties of each Nature being preserved, and (both) concurring into One Person and One Hypostasis; not as though He was parted or divided into Two Persons, but One and the Self-same Son and Only-begotten God, Word, Lord, Jesus Christ; even as from the beginning the prophets have taught concerning Him, and as the Lord Jesus Christ Himself hath taught us, and as the Symbol of the Fathers hath handed down to us.”
— Bindley, T. Herbert, ed. (1899). The Oecumenical Documents of the Faith. London: Methuen, p. 297