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The Sisters of Battle are an exception. They were formed as the fighting arm of the Ecclesiarchy, because the Ecclesiarchy was supposed to have "no man under arms". Warrior nuns kinda solved that problem for them.
I love all the double-reading and thin-lining of the rules of 40K life. Also, how one of the requests of the Emperor was that he not be venerated as a god, yet how after the heresy, it's a sin to not acept him as your personal god. Resulting, in several Chapters being under scrutiny from the Ecclesiarch, as they view him as a great commander and father of their primarchs, but not as a god.