What is the theme in Dark Force Rising by Timothy Zahn?

Running through all the Star Wars stories is the great power of the Force. In Dark Force Rising it is examined closely in two ways. Luke Skywalker, a haphazardly-trained Jedi Master, has come to fear that using the power to control human minds could move him towards the Dark Side, which consumed his father, Darth Vader, and the Emperor Palpatine, so Luke restricts its use.