These two insignificant children forge their own path, regardless of what everyone wants them to do. They disrupt the "proper" order of how things should happen by letting the dead out, getting separated from their dæmons, and changing the essence of the world through their roles as Adam and Eve.
Now that I'm older, the heavy biblical significance is much more noticable. I still love this book, but there is now a deeper meaning behind it. I still highly recommend it, however, please take the symbolism with a grain of salt.