First of all -- what did you think of the book? I think if you are going to write something about it and need a thesis statement, this is a crucial question. The novel revolves around a man who has a tragic thing happen to him while on a family vacation. His daughter is kidnapped and killed by a serial killer called "The Little Ladykiller." It plunges the man, Mack, into severe depression. He receives a letter signed by "Papa" asking Mack to meet Papa at "The Shack." Mack goes to the meeting and encounters God, Jesus and the Holy Spirit. Papa (God) turns out to be an African American Woman (very anti-Biblical from a theological point of view).
After long conversations with God, Mack drives home and is almost killed in a car accident. He wakes up and finds he never really even went to The Shack. However, he leads the police to where his daughter's body is hidden (in a cave, which was revealed to him by Papa), and the killer is caught.
But, back to the thesis. If you are a religious person reading the book, you may find all sorts of doctrinal problems with it. Although on the surface it seems to be a "Christian" book, it really has some far out views of God. So, if you are more traditional, you might want to center your thesis around how off-base the book is with regard to presenting God. If you want to use this approach, do some research. You will find that some heavy-duty Christian writers, like Charles Colson, have blasted the book for its "silly" portrayal of God. Your thesis could be center around "theological errors in The Shack."
If you thought the book was helpful and inspiring, in spite of the theological errors, you could have a thesis something like "Finding God in The Shack need not require theological soundness" and then write about how Mack's quest to find God helps him to heal and find forgiveness.
See the two links below for two opposite views of this novel.
Well you could go several ways on the topic of the thesis. It all depends on whether you agree with the book or if you think it's a load of garbage. I personally found it as a very moving book and i sort of believe on the topic of God but i don't agree with the views of god as a woman. Many a time I have gone back to read The Shack when i was in a meloncholoy mood, and the book keeps on enlightening me so read the book again and see how u feel on the topic of God and there's your thesis.