When did Space Marines become more 'religious'

Question

I know 10,000 years is obviously a long time, but the Emperor decreed he was not a God and many of the Loyalists legions upheld this belief, though some obviously worshipped him slightly in secret. In 40K many of the legions now seem more religious and indeed do see him as a God. Was there a pivotal point that caused this massive mindset change?

Obviously after the Emperor was first placed on the Golden Throne, I'm sure the surviving Primarchs would have tried to continue to spread the Emperor's Imperial Truth and that surely some of this would have been passed down in their teachings to the new chapters, especially as these would have been formed from those who were aware of the Great Crusade etc. And although I know no Astartes have survived to the present 40k time, they surely would have passed on the history of their legions and the crusades and with Astartes meant to have super memories, they should remember this in their training and pass it onto each new recruit. In 40k we also have Bjorn the Fell-handed who surely would also know about this (admittedly he spends most of his time sleeping now) and speak out against it?

Was there a pivotal moment as such that changed this? Or could it in fact have been the placing of the Emperor on the Throne that caused this? i.e totally destroyed in body, yet living on meant that even the Astartes began to worship him as a God, despite what I can only assume, would have been against the will of the surviving Primarchs?

Answer 1

The Imperial Cult, which states the Emperor of Mankind is a God was made the official religion of the Imperium in the 32nd Millenium. However, it's roots reach to times before the Horus Heresy - during the Great Crusade, Primarch Lorgar wrote Lectitio Divinitatus, a book describing the Emperor as a Divine being, a God. At first hidden, but as soon as Emperor was entombed in the Golden Throne billions of believers sprung up - the Emperor vastly underestimated Mankind's need to believe in something larger than them.

When did Space Marines and the rest of the Imperium became so religious? Most of them believed the Emperor was a God all along, many cults appeared as soon as the Emperor took charge of the Imperium, despite his insistance on the opposite, and condemnation of the Lectitio Divinitatus.

For normal citizens, the culminating point was Emperor's sacrifice at the end of Horus Heresy. For Space Marines as a faction, they never officially accepted His divinity, even if many of them do believe.

Point is, people needed to believe in something, the Emperor is a perfect target, and facts nor testimonies were not going to stop that. People simply wouldn't listen.

Answer 2

Even before the Horus Heresy the Word Bearers Legion began to worship the Emperor as a God, indeed this, at least in part laid the foundations for the Horus's eventual rebellion.

Also the Thousand Sons pursued research into psychic powers even after this was forbidden by the Emperor, although there is a reasonable argument that Magnus never intended to betray the imperium untill Horus duped Leman Russ into razing Prospero, probably because he saw a loyalist psyker legion as his biggest threat.

So one of the big sources of tension in the early Imperium during the great crusade was that the Imperial Truth declared any sort of religion false, but chaos entities were able to pass themselves off as gods.

Here the Emperor had a dilemma as he knew that the Chaos 'gods' fed off belief and indeed the whole point of the Great Crusade was to defeat Chaos by cutting of their access to belief by eliminating superstition from the whole of human culture. Unfortunately the message that 'gods to exist but acknowledging their existence will ultimately destroy humanity' is quite a hard message to get across. This was compounded by the fact that several primarchs discovered the existence of Chaos independently without understanding the threat it posed and were manipulated by it.

There is also a reasonable hypothesis that Chaos's plan all along was not to destroy the Imperium but to manipulate it into a semi-stable state where the original concept of atheistic 'Imperial Truth' mutated into a cult of superstitious emperor Worship which would provide the undirected belief that they needed and could exploit.