Ask the other readers what effect reading "The Shack" has had on their faith. Since this is a primarily Christian book, first establish what religious faiths each reader follows, then move on to discussing whether or not they felt reading the book challenged or strengthened their faith and why it was so.
Expand the discussion by asking readers to refer to the passages in the book that they found most moving. Ask readers what it was about these passages that spoke to them. If readers do not have passages of their own marked off in advance, share some passages that you bookmarked.
Look at the different ways God does and does not conform to traditional Christian thought in the book. Ideas include looking at God's female gender, the explanation that is given for the existence of the trinity, the existence of evil and the principle of forgiveness.
Close the discussion by asking readers to share their overall thoughts and feelings on "The Shack." Invite the group's members to raise any questions they had while reading the book or any other points they think are worthy of discussion.