It is indeed the same faith. We have way too much in common to be calling each other heretics and heterodox, and banning each other from our places of worship. I've noticed this predominantly among new converts to EO, or EO in the west.
There is an early 16th century Armenian Orthodox monastery/church complex in Romania (Oriental Orthodox, not EO). Romania is a very devout EO nation, and yet this monastery has become so popular among the EO faithful of the region, that they arrange [almost weekly] pilgrimages to visit the monastery and pray alongside the Armenians – the pilgrims are comprised of Romanian laymen and EO priests. It has had such traffic in recent times that the Armenian Apostolic Church has arranged for an Armenian priest to always be on-site and offer prayers in Armenian and Romanian. Are all those devout and faithful Romanian EO members destined to hell for identifying a fellow Apostolic Christian Holy site and choosing to pray with them to our Lord and Savior, Jesus Christ? Are they grave sinners for what Fr. Peter Heers (himself, a convert to EO) would call “praying with the heterodox?” This was the same mindset that drove Roosh to ban or warn anyone who did not fully align with his branch of EO. A lifelong EO faithful in Romania has no immediate fear of falling away and demonstrates more love and charity for fellow Apostolic Christians who are essentially following the same faith.
But back to the topic at hand. While I agree with
@KulturedKaveman on us essentially having the same faith, I do disagree on the language aspect. St. Cyril of Alexandria who formulated the Christological doctrine, wrote and preached in Greek. The School of Alexandria spoke and worshiped in Greek. The Copts are the heirs of Alexandrian Christianity and they are OO, in full communion with the Armenian Apostolic Church.
St. Cyril of Alexandria, whom we all venerate as a Saint, clearly defined the nature of Christ after the incarnation/union, and it was accepted at the Third Ecumenical Council at Ephesus in 431 AD. St. Cyril introduced his 12 Anathemas (accepted by our Church), which clearly defines the incarnate nature of our Lord. The dissent in the west arose after the Fourth Ecumenical Council at Ephesus was called in 449 AD by Emperor Theodosius II and presided by Pope Dioscorus I of Alexandria (himself, a protégé of St. Cyril) to reaffirm the Miaphysite doctrine of St. Cyril and to reaffirm his 12 Anathemas. Leo, the Bishop of Rome, who is not a considered a Saint in our Church, either through political motives or a complete misunderstanding of the matter, rejected the Fourth Ecumenical Council at Ephesus and persuaded Emperor Marcian (who had just ascended to the imperial throne) to convoke a new council at Chalcedon.
Now, why do we believe that Leo may have misunderstood St. Cyril’s Christology? Here is an excerpt from the Tome of Leo:
That paragraph, ends with a footnote explanation by Rev. Dr. Richard Price, a retired Catholic Priest and a prominent Roman Catholic scholar:
The above texts are from the English translation of the Acts of the Council of Chalcedon (Volume 2, Second Session, Page 23).
Another one, post-Ephesus I, and prior to Ephesus II and Chalcedon. This shows that Leo’s misunderstanding was bordering on Nestorius’ definition, rather that of Cyril’s – here is from Leo’s Sermon 54, given on Palm Sunday in the year 442 AD:
Source is the book “Sermons - St. Leo the Great” published by the Catholic University of America Press.
Because neither Eutychus, nor Leo, appeared well-versed in correct Christological argumentation, we ended up with this division, whereby the (current-day) OO communion saw Chalcedon as departing from established Orthodoxy and rejected the council. The OO churches continued dialogue with the Byzantines to arrive at a common understanding, but geopolitics and the arrival of Islam on the scene and in the area pretty much put an end to it.
So it was most likely Leo either didn't grasp the theological formula in Greek, or he was trying to recapture the Nestorian exiles of the time by appeasing them (as in the quote, above). We'll never truly know. However, there are hard-liners who have dug in trying to defend their positions.
@GoodShepherd I just wanted to note that I greatly admire your zeal and passion for the faith. I love the excitement which is apparent from your posts as you continue to learn and expand your knowledge. God Bless You, Brother.