From what I've read so far--of the book and the introduction--Diderot certainly does have a problem with the Catholic church--but not without cause. This novel may be an extreme case but evidently is based on real examples of how the Catholic church and society treated women at the time.
Why do you think Diderot wrote this book?
What does the book reveal about the role of women and the church in the time it was written?
Does he have a problem with the Catholic church?
How does the idea of illusion play into the story?
"The Nun" appears to be a traditional novel in many ways and yet in some ways it isn't.