Lewis takes the readers on a fantasy bus ride from hell to heaven, and describes what he believes to be the fundamental difference between good and evil, and the difference in traits between people in heaven and hell. I like the way Lewis uses imageries to illustrate theological concepts, and the dialogues of his characters are also very entertaining and revealing.
During the bus ride, one encounters all sorts of people from hell, an opportunistic businessman, a jilted poet, a possessive mother, a manipulative wife, a self-pitying husband, an artist who would rather paint heaven than live there, etc., the type of people one normally meets on earth.
Lewis combined Hell and Purgatory in one “place”. If the person never leaves, it will be Hell to him, but if he leaves, it will have been Purgatory. So the choice lies in the individual. Hell is a “state of mind”, and people who are in hell are imprisoned by their own self-centeredness. “Evil can be undone, but it cannot develop into good.” Unless they abandon their earthly(hellish) passions and desires, they cannot reach heaven where Light and Love abide.
“Life is not like a pool, but like a tree. It does not move towards unity but away from it. And the creatures grow farther apart as they increase in perfection. Good as it ripens becomes continually more different not only from evil but from other good.”