alt Hacker NewsWhich is to say, the original authors didn't care and were just writing latinesque gibberish that sounded cool.
One of the critically important things to remember about 40k lore is that the game was originally a joke. Their "real" game was Warhammer (the game to be later called "Warhammer Fantasy"). Originally it was just "Let's put space opera tropes onto a game board and have them fight D&D monsters". Then they shoe-horned the chaos stuff in, then had a (presumably drunken) exercise in lore writing where they "invented" "Grimdark" by essentially turning the Despair knob up to 11.
And then it turned out to be popular, and it was time to start trying to write real stories on top of the mess. And... people loved it. Including a lot of people for whom the comically ridiculous Grimdark stuff turned into a kind of authoritarian wish fulfillment, which wasn't great. But you have to remember it was all a joke to begin with.
It was more than just a joke. It was a satire on England and 1980's society.
The "Imperium," which is led by the possibly-dead body of a entombed demi-god, sustains its control over the galaxy with a mix of intense faith, authoritarianism, and a massive space navy with marine shock troops.
That's England! The Imperium is the British Empire. The dead-God Emperor is Jesus and the Imperial Cult is the COE. The Imperial Navy is the British Navy and the Space Marines (who in the older versions were just common criminals, not super-soldiers), are the British Naval Marines.
One of the old slurs against Christians was that they followed a "corpse-god." They say the same thing in 40K.
Plus, all the rampant materialism, corruption, stratification, militarism, promoted and encouraged by the Imperium. All straight out of 1980's society.