Why does this interest me?: Religion in warhammer 40k has had far reaching effects on the overall universe, from the near collapse of the 2nd human empire, to how the lives of the common citizens are held under its grasp. Of note though, things where not always like this as for the most part the Imperium was secularist in its past. Also, the Imperial cult was made by one of the emperor’s sons whom was deeply religious, wrote a book about how the emperor should be a god, which he found to be appalling.

What does this have to do with sci fi?: while the “imperial cult” has its normal influences on the common folk such has common worship,pretty much anything being heresy, it really comes down to how technology is influenced. See in Warhammer 40k, innovation is seen has a sin because one does not know the ramifications of his own invention, and as such, any time something new is needed, it can only be built and used for a single purpose, and this use has to be specific to the point of OCD. A.I. is also seen as another sin due to one taking power into his own hands to make intelligence. though some A.Is are allowed as the form of “machine spirits” which are amalgamations of machine and some organic material, in order form them to work one must chant “prayers” to them in order from them to work, or to be less temperamental. a good way of viewing them is a sort of chained A.I. that is to say, they do have some sentience and can gain complete autonomy if told to self destruct.

Sources: Horus Heresy Mechanicum army list. Warhammer 40,000 7th edition. the Horus Heresy novel series.