Origin: From what I am noticing it's just an extension of the Roman Empire and Vatican. Just check out the name Patri (Patrician) Arch (archon). Speaks for itself. The name certificates that go into the soul registers of the churches after baptism most likely end up in the registry of the Vatican. There is the White Brotherhood sect who promotes true Christianity, the way it was practiced by the Cathars who were wiped by the Inquisition. Recently in one of their books I found the term "black brotherhood". Nothing else resembles the black brotherhood more as the organised church in the east. I think they are part of the Vatican. After all, it used to be Eastern Roman Empire....the root is the Roman Empire.

Function: To keep the illusion of spirituality in the East. To make incognito satanic rituals disguised as Christian rituals. To hold onto land and real estate and be parasites to the plebs/slaves. To register the souls/names of the slaves in the registry of the Vatican. To support the state.

This is my opinion. Open to change my theory if more info is presented. Thank you for the question!