Religion in the Realm of Iurrran
The primary religion of the Realm of Iurrran has grown out of a combination of the mystical practices of the original Iurrran people, the traditions of the Hounds of Iurrran, and a form of the Imperial Truth. The Iurrran religion's relationship with the supernatural is primarily transactional, it recognized the existence of four 'great powers' which are not worshiped but are respected as the lords of the four main types of daemon kind. Independent warp entities, such as unaligned daemon princes and minor godlings, are also recognized in the form of lesser powers.
The church itself is comprised of a combination of bureaucrats and shamans. Shamans are trained psykers provided blessing by trading favors with the spirits. The bureaucracy is designed to manage the church's affairs and oversee the shamans.
The cult of Horus:
Prior to the formation of the Hounds the Iurrrans did not worship any entities however the Hounds' reverence for their gene father has since been incorporated into the religion. The Lupercal is revered as a lesser power and a guardian of humanity.
According to legend, the Emperor is considered a powerful psyker who attempted to conquer humanity to bend to his own whims. In order to do this, he created the primarchs, with the Lupercal as the first and greatest of them. Once he discovered the Emperor's plans and his place in them Horus rebelled, forging pacts with the great powers and leading his most trustworthy brothers against the tyrant to free humanity. Both the Lupercal and the Emperor were killed in the climatic confrontation, though not before the human homeworld was devastated.
Cults of the four:
Cults dedicated to the major chaos gods are not unheard of in the realm of Iurrran. They are however, monitored and kept on a leash by the church bureaucracy which use them as a source of sacrifices for rituals and a bargaining chip to use in making deals.
Have a world building Omake