i'l be glad to try and answer that for you
it's not something you set out to memorize really but it's something you learn and apply to your life. the bible isn't actually just one book but it's a collection of books from different authors over centuries and centuries (with the latest being something like 200AD i think).
and these books are put together to form the bible because christians believe that their writing was 'god-breathed' that is, their ideas agree with and represent god's very own ideas.
so, if you try to put yourself in a christian's shoes, you can imagine that you would want to know what god is trying to tell you - through the bible.
i hope that's simple enough =]