One piece of advice - the nature of The Cause is irrelevant. It is not a film about that and it never was. It's not an expose on religion or Scientology. Rewatch the film ignoring that and you will see it differently.
What is Freddie Quell? What are his motivations? What does he represent? The incredibly disciplined screenplay and performance asks these questions without answering them.
That is the genius of the film. For once you are not being told how to feel about the subject - it is what it is. Quintessentially post-modern, I found it to be mesmerizing.