The fourth ecumenical council that convened in Chalcedon became a turning point in the history of the Armenian Church, even though the Armenian Church was not represented at Chalcedon.
The first ecumenical council at Nicea (325) determined that Jesus Christ was God, “consubstantial” with the Father. This meant that God (Father, Son, and Holy Spirit) are “of one being” in that the Son is “born” or “begotten” “before all ages” or “eternally of the Father’s own being, from which the Spirit also eternally “proceeds.” The confession of Nicea, recited in every Holy Mass of the Armenian Church, states: “We believe (...) in one Lord Jesus Christ, the Son of God, begotten of God the Father, only-begotten, that is of the substance of the Father (...) who for us men and for our salvation came down from heaven, took body, became man, was born perfectly of the holy Virgin Mary by the Holy Spirit. By whom he took body, soul and mind and everything that is in man, truly and not in semblance.”
This was reaffirmed at the first council of Constantinople (381) and the council of Ephesus (431). One of the fathers of the Church, Cyril of Alexandria (d. 444) taught that “There is only one nature (physis), since it is the Incarnation, of God the Word,” which was held as orthodoxy.
In 446, an aged monk from Constantinople named Eutyches started teaching a subtle variation of this doctrine. His teachings were considered heretical, but he was rehabilitated in a council marred with scandal, held again at Ephesus (449) and supported by Byzantine emperor Theodosius II (408-450) where he publicly professed that while Christ had two natures before the incarnation, the two natures had merged to form a single nature after the incarnation. Pope Leo I denounced the council as a “synod of robbers” and refused to accept its decisions.
The threat of a schism led the new Byzantine emperor, Marcian (450-457), to hold a new council at Chalcedon (451) from October 8 – November 1, 451, which condemned the work of the council of 449 and professed the doctrine of the incarnation presented in Leo’s Tome, a document prepared by the Pope, which confessed that Christ had two natures, and was not of or from two natures. A special committee appointed by the Council decided unanimously in favor of the orthodoxy of Leo’s Tome, and determined that it was compatible with the teachings of Cyril of Alexandria. The confession of Chalcedon stated: “We, then, following the holy Fathers, all with one consent, teach people to confess (...) one and the same Christ, Son, Lord, only begotten, to be acknowledged in two natures, inconfusedly, unchangeably, indivisibly, inseparably.”
The formula on the nature of Christ adopted by the Council of Chalcedon was severely criticized by various Oriental sees. Many local councils rejected that doctrine. Resistance reached the point that Byzantine emperor Zeno I (474-491) issued a document called Henotikon in 482, which considered the doctrinal resolutions of the first three councils (Nicea, Constantinople, and Ephesus), while the Council of Chalcedon and Leo’s Tome were not mentioned at all.
At the time of the Council of Chalcedon, Armenia was in crisis. A few months before, in May 451, the battle of Avarair had been fought, and the Armenian Church was in no position to have its say on the issue. The situation changed after the Treaty of Nvarsak (484), when the situation stabilized with Persian Armenia under the government of Vahan Mamikonian. The Armenian Church adopted the doctrine of the Henotikon, and this position was officially confirmed by the Council of Dvin (506).
The followers of the Council of Chalcedon have frequently accused the Armenian Church of monophysitism, but this is not true: the Armenian Church follows the doctrine of Cyril of Alexandria established at the third ecumenical Council of Ephesus (431) that reaffirmed the decisions of the Councils of Nicea and Ephesus.