Basically, if there is a 'reason' for something it either has to be true or at least makes sense for whatever the scene is. Most of the original trilogy in part when the force is mentioned, you don't see it, but it is possible to its capabilities, such as Yoda or the dark side cave; I think that to a lesser extent the force and the dark side is not entirely important so to speak, more or less what you see as a result. Vader, the emperor, Luke, Yoda and Obi won how the emperor acts as a temptor near the end, including Vader.
I wish Lucas had been more detailed certain sections. There's form, but not enough detail in-between.