Star Wars: The Return of Darth Vader

On the rebel base on Endor, the rebels get a message from Vader stating to turn Luke over to them, or the base will be destroyed. It is unclear what the true reason to why the Empire is so desperate to capture Luke, maybe it is because he was the pilot who destroyed the death star. Or is it something else? Discover Luke's future and his battle against the darkside and the Sith.