The Ecclesiarchy, also known as the Adeptus Ministorum, is the state religion of the Imperium of Man, based on the widely disseminated Lecitio Divinitatus that proclaimed the divinity of the Emperor. The church mandates the worship of the Emperor as the savior of humanity and the uniter of its massive empire. It is an extremely powerful organization that can leverage its influence by labeling detractors as heretics, a crime punishable by death. Unknown to them or the Imperium at large, the Lectitio Divinitatus was written by Lorgar prior to the Horus Heresy.
After the Reign of Blood, the Ecclesiarchy can no longer maintain its own military force. However, on a technicality, it maintains a seperate order called the Adeptus Sororitas, an all-female sect that sidesteps the prohibition of men under arms. They serve as guardians of holy sites and prosecute the purging of heretics on many worlds. In this capacity, the Ecclesiarchy works closely with the Inquisition's Ordo Hereticus.