The Imperial Cult, the state religion of the Imperium of Man worshiping the God-Emperor has undergone significant evolution from its inception to the current timeline.
Unification Wars
Before the establishment of the Imperium, the Emperor led the Unification Wars on Terra, aiming to consolidate the warring techno-barbarian states under a single banner. During this period, the Emperor suppressed various religious practices, culminating in the purge of the last religious center on Terra, to establish a secular foundation for humanity’s future.
The Imperial Truth
During the Great Crusade at M30-M31, the Emperor of Mankind promulgated the Imperial Truth, an atheistic doctrine emphasizing science, reason, and the rejection of superstition, worship and religion. The Emperor sought to unify humanity under this secular philosophy, eradicating religious beliefs that he deemed divisive and regressive.
Lorgar and the Emperor
Future heretic and traitor Lorgar Aurelian, Primarch of the Word Bearers Legion, held deep spiritual convictions and viewed the Emperor as a divine figure. He authored the Lectitio Divinitatus, a text proclaiming the Emperor’s divinity. Displeased with Lorgar’s deviation from the Imperial Truth, the Emperor reprimanded him and ordered the Ultramarines to destroy the city of Monarchia, a model of Lorgar’s religious devotion, to serve as a lesson against deification.
Emergence of the Lectitio Divinitatus
Despite the Emperor’s efforts, a clandestine religious movements around Lectitio Divinitatus emerged, venerating the Emperor as a divine being. These cults gained traction among various segments of Imperial society, including some Space Marines.
“Rejoice, for I bring you glorious news,
the God walks among us.”
First lines of Lectitio Divinatus
“The strength of the Emperor
is the humanity.
The strength of the humanity
is the Emperor.”
Excerpt from Lectitio Divinatus
Guilliman Bans the Book
Roboute Guilliman, Primarch of the Ultramarines, recognized the potential dangers of the Lectitio Divinitatus. Concerned about its divisive nature of worship and the deviation from the Imperial Truth, he took measures to suppress the spread of the text within Imperium.
The Horus Heresy and the Rise of the Imperial Cult
The Horus Heresy, a galaxy-wide civil war initiated by the traitorous Warmaster Horus at M31, profoundly impacted the Imperium’s philosophical landscape. Even disillusioned primarch Lorgar, the original author of Lectitio Divinatus, persecuted the emerging Imperial faith. Yet, in the aftermath of the Heresy and the Emperor’s internment in the Golden Throne, the belief in the Emperor’s divinity became more widespread. The Lectitio Divinitatus evolved into the Imperial Cult, consolidating various Emperor-worshipping sects into a unified state religion.
The Temple of the Saviour Emperor and the Age of Apostasy
In the subsequent millennia, the Temple of the Saviour Emperor emerged as a dominant religious institution, eventually formalizing into the Adeptus Ministorum, or Ecclesiarchy. However, the Ecclesiarchy’s increasing power led to corruption and abuse, culminating in the Age of Apostasy at M36. This tumultuous period was marked by the tyrannical rule of Goge Vandire, who exploited his positions as both the Ecclesiarch and the High Lord of the Administratum. His reign was characterized by widespread persecution and internal strife.
Sebastian Thor and the Reformation
The tyranny of Vandire was challenged by Sebastian Thor, a charismatic preacher who rallied opposition against the corrupt Ecclesiarchy. Thor’s leadership led to Vandire’s overthrow and significant reforms within the Imperial Cult. The Ecclesiarchy was restructured to prevent future abuses of power, and Thor’s teachings became foundational to the reformed Imperial Creed.
The End Times Eschatology
In the current era at M41, five thousand years after Thor’s preaching’s, eschatological beliefs are gaining prominence within the Imperial Cult. Prophecies and doctrines concerning the End Times have become central to prominent reformers of Ecclesiarchy and doomsday prophets of fringe sects like Polarists, Pyreans or Red Redemption, influencing both religious practices and the Imperium’s governance.
Excerpt from Guy Haley: “Plague Wars”:
“Guilliman flipped open the lid of the box. The book was slender and rested inside a shallow compartment bathed in the still light of the stasis field. It was so old, almost as old as him. Together they were relics of another age, time-lost things. In appearance the book had nothing that suggested the power it possessed. But it was powerful, and so disruptive that Guilliman himself had banned it after Horus’ betrayal. Every copy that could be found was burned, its words deemed tainted with a traitor’s lies. It was expunged from history, scraped out of the record. People had died to protect it. The faithful called them martyrs, but the Imperial Cult had been small and ridiculous and he had ignored it. By then, the damage had been done. The thoughts were out, a memetic virus spread from mind to mind. It had no cure. The writings in this book, the thoughts and beliefs of an arch-traitor, were the foundation of the Imperial Cult. He speculated if the high priests of the Ecclesiarchy were aware of this fact. Often the book was poorly printed, dashed out of underground presses in furtive acts of samizdat. This one was finely made, the property of a rich man or woman. That could have explained why it had survived.
The lonely title was emblazoned on the cover in flaking golden leaf stamped into light brown leather. There was no author’s credit. The skin oils of its owner stained the lower right-hand corner of the cover. The sole trace of a person ten millennia dead; the book had been read many times. Guilliman wondered what manner of person they had been. Imagining was a fruitless exercise that yielded an infinity of theoreticals with no resultant practicals. A waste of time. He cut dead the trains of thought. Imperial Gothic had evolved since the book was written; even the highest, most ossified form had been dragged out of shape by the tides of change.
The script on the book was of the oldest kind. Reading it brought a sudden flush of memories to the primarch. They intensified Guilliman’s feelings of displacement, and he almost abandoned the idea in favour of destroying the book and its box. He did not. His finger depressed the hidden stud, shutting off the stasis field. He stared at the book some more. He picked it up. The leather was dry and flaking. The paper smelled as old paper does: a fusty sharpness, the smell of hidden wisdom and dying memories. Ten thousand years after Lorgar Aurelian set pen to paper to create this tract, Guilliman began to read it. Rejoice, for I bring you glorious news. God walks among us. So ran the first two lines of the Lectitio Divinitatus.”
Ignis Aeternus WH 40K campaign notes 