I'm not a big fan of the overloading of the term "bible" in a lot of contexts. It's not from any kind of religious offense or hurt, though. It's more of a clarity thing. I had a friend once say, out of nowhere, that she'd been reading "the bible", by which she meant "Men are From Mars, Women are From Venus". I've heard the primary documentation on software projects referred to as the "project bible", which always gets shortened to "the bible", and it always takes me a few seconds for my brain to latch onto the real contextual meaning rather than the one with which I am automatically most familiar (the actual Bible).
My point is that communication is supposed to be clear, although poetry can sacrifice clarity for emotion. When you refer to some other book or document as "the bible", you are probably being just a little bit too poetic, sacrificing just enough clarity for the sake of your point about the importance of that book.
Mokalus of Borg
PS - We'll all know how important a document is, in context, from experience with it.
PPS - Or because you say "this is our most important document".