I think they do. It is very sad, actually.

I think a lot of them don’t even KNOW what’s in their book

Some do, and many simply believe that it is a good idea to believe but don't actually believe. There are those who don't believe but will never admit it.
I am ashamed to admit that due to my childhood indoctrination I at one time did REALLY believe and would have died if someone put a gun to my head and told me to deny my beliefs. No kidding. There are real believers and there are also liars. It is often hard to tell the difference.

They believe what ever they cherry pick out of their holy book that happens to match their already present world view.

they say they do, and yet so few of them have actually read either the christian bible OR the jewish bible, on which their "old testament" is based (no, they're not the same thing).

g