Tou may want to talk to the Orthodox church about that.
No mystery.
The Orthodox Church split away from THE church, only after that was it necessary to state Roman to describe the remaining catholic universal church,
Having first accepted the " primacy of honour" of the bishop of Rome, indeed - from iraneus even to Augustine listing the popes as authority ( that case on donatism) , the eastern s went their own way.
They clearly split from the root. They are not the root that believed in and stated in council the primacy of Rome,
The schism almost healing but for a vote of one centuries later...
a few arcane theological differences too.
Like ....they accept as they must the real presence, indeed in the liturgy quoting Justin Martyr, saying " is the flesh of Jesus" they leave as a mystery how, preferring not to state that by simple logic If it was bread, is now flesh, it therefore by definition changed substance, or,
They accept as they must that only pure things get to heaven, knowing they are not, but do not go the next step and leave as a mystery that their must have been a process of purgation / theosis, in which prayers after death are effective , we name the process or state purgatory, but otherwise say little about it,
In short they leave as a mystery, things we give a name to.
Or the even more arcane matter of Filioque.
Few can understand it, let alone argue it!
Then much misunderstood area of original sin. The problem is most of the analogies like " stain" misrepresent catholic theology, which in reality in essence declares the absence not the presence of a something, and so create a wedge of assumed division where there is little.
But compared to the rest of the post reformation. Churches our theological differences are small.
Because orthodox unlike most post reformation churches retain early church fathers and council decisions, they just fractured into a variety of autonomous and autocephalous churches. So are not the origin, athough they remain faithful to most of the theology.
I love orthodox / eastern spirituality, and much prefer their celebration of such as advent.