I wish I understood it better and what they based it on - in the 4th century, not knowing Jesus, they were debating about his nature.
What did they have to go on? Scripture? Tradition? Just ideas that came up in the moment?
Well, a dialogue with Scripture, based on Tradition.
It's essentially a philosophical debate, and it can become technical and complex, and invariably did ... but it does have significant ramifications.
For example, Jesus is God, Jesus is also man. Is that two persons, or one person in two natures? One soul or two.
What it boils down to is, did Jesus, being God, subsume the human person of Jesus so there was nothing of the man left? Does it metter, well yes, it does, because the answer to that determines what we mean by an afterlife.
A common idiom is the idea of the self uniting with the One as a 'drop in the ocean' – but then does the drop lose its entire identity? Is the drop not extinguished by the ocean ... ?
(The mystical answer is, of course, a paradox ... )
Indeed, it would be interesting though. For example what Mormonism might have become if they had access to this material, or if Seventh Day Adventists or Jehovah's Witnesses did. I don't know if maybe the Armstrong churches did, their Binitarianism is, I think, a return to something pretty old that hadn't been revisited even though Unitarianism and variations of Arianism has been I think...
The Ethiopian Church did not have access to any material that wasn't and isn't in the Church as such – the video says:
"a different version of heaven's greatest war has survived untouched by Western doctrine."
"According to the Ethiopian Orthodox Tuhedo Church, the battle between the angelic forces of good and evil was not simply a matter of prideful rebellion as portrayed in European texts ..."
Hang on ... 'Europe' is an anachronism here, and is used to set up an artificial divide.
"... but a test of loyalty to a divine mystery. One that involved the revelation of a future creation, humanity. Ethiopian tradition claims that before the material world was formed, God convened the angels and revealed to them his plan to create man in his own image. It was then that the angel Satinel, once called the bearer of light, rebelled not out of pride alone, but out of disdain for the idea that a being of clay and breath would be exalted above him."
The 'bearer of light' image I think is erroneous, assuming too much of a Lucifer interest ... and to say the rebellion was not out of pride, but disdain, is nonsense, because what gave rise to the disdain, but the idea that the angel thought himself better than human?
This is not unique to the Ethiopian Church ... it was common to Jewish and early Christian thinking.
"While Western Christianity teaches that Lucifer's downfall was rooted solely in hubris, the Ethiopian version introduces a more layered conflict."
and then goes on to describe the angel's hubris, without actually using the word.
+++
The introduction of the Archangel Michael, and so on ... all common knowledge.