What is the Force in Star Wars? Is it based in magic and spirituality like the original trilogy seems to imply? Or is it based in science like the prequels state? Is the Force even real? Without the help of the Extended Universe, and only the movies as one's guide, the average viewer most likely left the theater after any given Star Wars movie wondering, "How does the Force work in Star Wars?" or, "Who discovered the Force in Star Wars?" or even, "What the heck is a Midi-chlorian?"
The Extended Universe goes to great lengths to answer these questions. Instead of a vague description of a magical energy field or bringing up Midi-chlorians without digging into what they are, the Extended Universe provides so much context and information that even the most dedicated fans don't have time to scope it all out on their own. That doesn't mean everything about the Force is fully explained, though; there is still plenty of room for fan theories about how it truly works. With that said, any questions about how it generally works, or what its connection to life and death is, or where it started, have been answered.