I’m not an expert on the Bible by any stretch of the imagination. I did read a few passages of the Book of Revelations as a younger man, out of sheer curiosity, but that’s about it. Still though, it’s a very interesting name, even if you haven’t read any of it.
It basically means the book. It’s derived from the Latin biblia sacra, meaning holy books. This phrase can be traced back to the Greek word biblion, meaning paper or scroll.
But while its older names meant the holy books, if you’re a Christian, it probably makes sense to think of it as the book. And with it being the book, it of course makes sense to capitalise it. The T of the isn’t necessary, but certainly the B. The first B, obviously.
Of course you don’t have to be a Christian to capitalise it. I’m not religious, but I do it. You could so out of respect, or simply because, like the title of any book, it’s a proper noun.
And it might be necessary to use the capital B to distinguish the book(s) from any use of the word bible as a regular noun. I might say, accurately, that English in Grammar in Use by Raymond Murphy is the English-language teacher’s bible. Or maybe something by Martin Parrott.
We can also see many modern words inspired by the Greek biblion, all related to books. If you cite a lot of sources in something you write, you should include a bibliography. The -graphy is from the Greek for written. But you already knew that.
And of course, if you like reading books, you’re a bibliophile, literally meaning book lover (compare to words like Anglophile, cinephile, and uh, yeah, that’s it).