Ah, The Great Divorce; one of my favorite C.S. Lewis novels! I have been reading it for the umpteenth time for the past week or so. This story is one surreal adventure involving a bus that goes between Heaven and Hell. The title is a reference to William Blake's The Marriage of Heaven and Hell. Lewis is writing of their divorce, which makes sense as sin cannot exist in Heaven. This novel shares a lot in common with Dante's La Divina Commedia, in particular the presence of a guide (in this case George MacDonald), how sin and salvation are represented allegorically, and a surreal setting. It shares a lot with John Bunyan's The Pilgrim's Progress (spoiler alert: in this case, it all being a dream).
The story opens with the narrator standing in line at a bus stop at dusk in a miserable grey town where it is always raining. The town goes on for miles on end and doesn't seem to stop. The narrator gets on the bus and is taken to a spectacularly gorgeous natural landscape, but finds that he can't even so much as bend the grass. In fact, it goes right through him and causes a lot of pain; he's a Ghost! As is everyone who got off the bus. There are radiant Solid People (most often called Shining Ones in the novel) coming to convert these souls, and one of them leads the narrator as he helps him understand the respective natures of Heaven and Hell.
One thing stands out is how so many of the Ghosts will not accept Joy because it means giving up their quirks, such as saying mean things to their loved ones or lording superiority over other people. There is one character who always considered himself to be a good man and can't understand why a convicted murderer is in Heaven whereas he is not. Another man used other people's pity as means to blackmail them in life and won't let go of that power in Heaven. And a possessive mother will quite cheerfully drag her son to Hell to her if it means she will keep him. They would much rather cling to their sins than accept God. There's a lot of insight as to how sin works and how grace works, and how ultimately there are only two types of people in the world: those who submit to God and those who don't.
And there is also quite a lot of talk about how hard Heaven is to those who are not saved. The Ghosts are insubstantial and just walking on the grass feels painful. But they can become solid by accepting God's grace and letting it change them. This is a very interesting concept.
Read it.