Originally Posted by
gorepants
The prayer aspect seems to owe a lot to the Buddhist style warrior monk as well. Certainly their fervour for the Emperor and the Imperium owes more to militant Christian traditions, but the agnostic/atheistic nature of their spiritual life seems sits closer to Buddhism. It's mostly driven at finding inner peace to more effectively kill stuff (the killing bit is not that close to Buddhism!), and doesn't require any particular God or gods.* They do however revere their work, their tools and their brothers. This also smacks of north European and Greco-Roman religions, which were much closer to tribal animism, and whose gods were much more human. In one of the newer short stories, a new Chaplain is chosen for his violent hatred of the enemy, not his devotion to the Imperial cult.
In short, marines are a hodge-podge of references, though in the fluff they do not (for the most part) worship the Emperor as a literal god.
* In practice the metaphor is mixed, since it would seem they have stripped away the mystical aspects of the imperial cult prevalent in the ecclissarchy, like Zen, but retain a fixation on ritual and litanies, like dharmic Buddhism.