Built upon the words of the Prophet, the Church sees to the spiritual and physical needs of the Pure. Being the only organization of any significant power among the humans living under the Eternal Darkness its power reigns unchecked, however, at least in this case, absolute power has not corrupted absolutely, only moderately. With missions found in every major community among the human 'lands' and roaming priests to see to the spiritual and earthly needs of those in the minor communities.
Order of the Sun - traditional clergy + added duties of judge, census taker, and tax collector. the cake job in the order is to get assigned to a fixed temple, to act as a local ruler/priest, however most jobs are of the wandering 'missionary' kind. This is the primary branch of the Church, and what most people think of when talking about the church. Higher levels are the bishops, ruling over larger regions, and the pope/caliph the head honcho for teh church.
Order of the Faithful - assassins witchhunters and spies, self references as teh knife of the prophet, never talked about, and feared to occupy every dark corner of the human world, and there are a lot of those, the Faithful are the inquistion of the Church, stamping out heresy where ever they find it, whether it be dogmatic heresy, with a single priest preaching that man isn't the author of his own destruction, or heresy of a viler sort, a sorceror among the populace.
Wardens against the Dark - the militant arm of the church, this is the army of the faithful waging a constant crusade against the slaves of the dark mother. Everyone is conscripted into the Wardens for a little bit in their life, to fight the hordes that threaten the existance of us all.