" Great actions have shaped our society.’ Sindermann said. The greatest of these, physically, has been the Emperor's formal and complete unification of Terra, the outward sequel to which, this Great Crusade, we are now engaged upon. But the greatest, intellectually, has been our casting off of that heavy mantle called religion. Religion damned our species for thousands of years, from the lowest superstition to the highest conclaves of spiritual faith. It drove us to madness, to war,
to murder, it hung upon us like a disease, like a shackle ball. I'll tell you what religion was... No, you tell me. You, there?'
'Ignorance, sir.’
Thank you, Khanna. Ignorance. Since the earliest times, our species has striven to understand the workings of the cosmos, and where that understanding has failed, or fallen short, we have filled in the gaps, plastered over the discrepancies, with blind faith. Why does the sun go round the sky? I don't know, so I will attribute it to the efforts of a sun god with a golden chariot. Why do people die? I can't say, but I will choose to believe it is the murky business of a reaper who carries souls to some afterworld. "
― Dan Abnett , Horus Rising (Horus Heresy #1)