Small Fluff Question (Purity Seals)

The emperor protects. In other words, I find it pretty obvious space marines also believe in the god emperor. Also, there definitely are acts of faith in the 40k universe, if anything, its a maybe a special kind of warp magic, as faith surely can shape the warp as emotions do.

Ketter

Keep in mind that think the lore portrayed here: https://warhammer40k.fandom.com/wiki/Imperial_Cult is pretty much canon (it coincides what I remember reading in 40k and Black Library resources) Read the below quotes I drew from it, from them it is pretty much clear that the Space Marines themselves are not really into the religious, i.e. Emperor veneration stuff. Magic being real in 40k only pertains to the warp, not to incantations sung and holy rites performed on machines and Space Marines suits being rubbed with sanctified ointments. Those are cargo cult religions, which just coincidentally help people work with machinery they no longer understand. This is actually a part where 40k lore is very nicely thought through I think. If the purity seals were to actually work, they would need to have something to do with the universes 'real' magic, i.e. warp energy, not the imperial religion, but that's not what they are. The only effect they can have is psychological in nature. I think the idea is to attach it to the thing they're supposed to have meaning for, so a seal for something abstract would not be canon - but mostly due to that having never appeared, not due to an obstacle in principle. "While the ordinary citizen of the Imperium believes that the Emperor has always been venerated as the immortal and omnipotent god of humanity throughout the history of Mankind, Imperial historians and the Battle-Brothers of the Space Marine Chapters know that this was not always the case. At the beginning of the Emperor's Great Crusade in the late 30th Millennium, the Imperium of Man functioned very differently. Firstly, there was no Ecclesiarchy, and the veneration of the Emperor, in the form of a cult known as the Lectitio Divinitatus, was frowned upon and outright condemned by the Emperor Himself. The official Imperial doctrine, known as the Imperial Truth, was that the Emperor was an extremely powerful being, the rightful ruler of all Mankind, and the perfect physical, mental and spiritual embodiment of humanity, but no matter how supreme, he was still only a human being. During the Great Crusade, however, many ordinary Imperial citizens found that the light of reason and truth brought by the Emperor was not enough to fulfill their basic human psychological desires or provide protection from the real supernatural threats that existed in the universe, and so they took to worshiping Him as a deity to fulfill their spiritual needs." [...] "This development culminated in the early 32nd Millennium, by which time almost two-thirds of the Imperium's population followed the teachings of the Temple of the Saviour Emperor, the exceptions being the Space Marines, who have never formally acknowledged the divinity of the Emperor in line with His wishes and the Adeptus Mechanicus, who had their own form of worship in the Cult Mechanicus. The Temple's importance, influence, and power rapidly outmatched any other Imperial sect dedicated to Emperor-worship."

Wolf Bullmann

This is the attention to detail that I love!!