In general, they believe that Christ is one Person in two hypostases and natures. And this is how they understand Nestorius and Mar Babai.
So, their Nestorius understanding is different from our understanding. That’s why we have common ground that Christ is one Son and Person.
You are correct, historically, although happily at present I am pleased to inform you, as someone who via an accident managed to be received in both the Eastern and Oriental Orthodox churches, and who opposes the continuation of that schism, but the Assyrians still have some problems, but are improving - whereas they did believe in Nestorianism in the 5th century, their stance has moderated. They now agree with the Chalcedonians and the Oriental Orthodox, that Christ is fully God and fully man, united in one person without change, confusion, division or separation.
The essence of the Nestorian heresy was the insistence of a division or separation between the humanity and divinity of Christ, so that the principle of communicatio idiomatum would not apply, and this flowed naturally from the root heresy of Nestorius, which was a milder form of the heresy previously identified by St. Epiphanios of Salamis in the 4th century Panarion , as Antidicomarianism, which is a refusal to venerate St. Mary. Nestorius believed the people of Constantinople venerated her excessively, and so to deprecate that, he persecuted with violence those who confessed Our Lady to be Theotokos.
However, there was a mishap at Ephesus, perhaps an intentional one, on either side, wherein the correct action of that council lead by St. Cyril the Great with the support of other bishops such as St. Celestine the bishop of Rome to depose Nestorius as Patriarch was made before some bishops from the Persian Empire arrived, and this resulted in a schism, although after Chalcedon, which Nestorius claimed to support in his memoirs “The Bazaar of Heraclides”, in which he was probably honest, as there was a crypto-Nestorian element, but Chalcedonian Christology thanks largely to the influence of St. Severus of Antioch on Emperor Justinian during his early years before Justinian began to persecute the holy Oriental Orthodox churches, especially the Syriac Orthodox, arresting and probably executing most of their bishops except for St. Jacob bar Addai, who was aided by Empress St. Theodora and avoided capture and acting solus as warranted by the emergency, ordained hundreds of bishops for what is now the Syriac Orthodox Patriarchate of Antiochl
But before Justinian renounced Theopaschite Orthodoxy in favor of a complex heterodoxy called “Apthartodocetism”, he did at least cause a lasting shift in Eastern Orthodox Christology by introducing the hymn originally composed by St. Severus, Ho Monogenes, which opens the Syriac Orthodox liturgy and is used by the Copts in Holy Week, and it was appended to the Second Antiphon of the Byzantine Synaxis, which later became part of the Armenian liturgy as well.
In English, this hymn is
Only-Begotten
Son and Immortal
Word of God,
Who for our
salvation didst will to be incarnate of the holy
Theotokos and
Ever-Virgin Mary;
Who
without change didst become man and was
crucified;
Who art one of the
Holy Trinity, glorified with the
Father and the
Holy Spirit:
O Christ our God,
trampling down death by death, save us!
[6]
I regard it as a proof of Christological Orthodoxy.
The Trisagion is more complex since in Oriental Orthodoxy, we understand it as being Christological, whereas in Eastern Orthodoxy, it is interpreted as Trinitarian.
This kind of misunderstanding later was repeated in the schism between the Russian Old Rite Orthodox and the Czar, because the Greeks, who Patriarch Nikon assumed were correct, make the sign with three fingers as a Trinitarian gesture, whereas the Russians traditionally used two fingers to symbolize the humanity and divinity of Christ. Fortunately that schism partially healed when the Old Orthodox stopped being persecuted and some, the Edinovertsy, re-entered into communion with the canonical Russian church while retaining the ancient Russian liturgy which we now know was not, contrary to what Czar Peter and Patriarch Nikon assumed, corrupt, but rather reflected an older recension of the Studite-Sabaite monastic typikon.
Unfortunately the Assyrians have not yet adopted this hymn, and this is one of the challenges they face theologically, but they have improved and are moving closer to us, and they do not confess the filioque.
These schisms are all very sad. But given the reconciliation between the Syriac Orthodox and the Antiochian Orthodox, and the Copts and the Alexandrian Orthodox (indeed, Syriac Orthodox can receive communion in Antiochian parishes in the Middle East, and Copts likewise usually can in the Greek churches of Alexandria, and vice versa, and also I have heard the monks at St. Catharine’s Monastery in Sinai will give communion to Coptic pilgrims.
So we have to pray for progress with the Assyrians, and I have heard it is happening between the Assyrians and the Russians.
By the way
@Tigran1245 , I am very curious, and I suspect so is our brother
@dzheremi , how things are between the Armenian and Russian churches at present.
