Conversation so far:
What role do priests play in Mandaeism?
There is a strict division between Mandaean laity and the priests.
What are the three grades of priesthood in Mandaeism?
There are three grades of priesthood in Mandaeism: the tarmidia disciples, the ganzibria treasurers and the rišamma leader of the people.
How does one become a priest in Mandaeism?
Any ganzeḇrā who baptizes seven or more ganzeḇrānā may qualify for the office of rišamma, though the Mandaean community has yet to rally as a whole behind any single candidate.
What are some differences between priests and laymen in Mandaeism?
There is a strict division between Mandaean laity and the priests.

Question: Why is there division?
Self-contained rewrite: Why is there division between priests and laymen in Mandaeism?