An open mind is like a fortress with its gates unbarred and unguarded

There is a full list of WH40K quotes here: https://wh40k.lexicanum.com/wiki/Thought_for_the_day_(A_-_H) – alongside other gems one can find “A logical argument must be dismissed with absolute conviction!”, “He who allows the alien to live shares its crime of existence” and “Hope is the beginning of unhappiness”.

The game is obviously satire, but I think the quotes talk to the power of fanaticism. Strong, unmovable beliefs can change the world.