The story is structured into five chapters because there is one for Christmas Even, one for each ghost and one for Christmas Day.
Dickens chose the name “carol” so he organized the story into staves, like in music. He wanted to emphasize that the story is very short and specific. Like many actual Christmas Carols, it has a moral. It is about living your best life, and as many carols, it is about the true spirit of Christmas, which Dickens believes is that we should take care of each other, and you can be happy no matter how much material wealth you have.
The first stave is Christmas Eve, and it shows what Scrooge was like before his visitation. He is a grumpy old miser. His dead partner Jacob shows up and offers him a rare chance to look into his life and see glimpses of the past, present, and future.
It is required of every man …that the spirit within him should walk abroad among his fellowmen, and travel far and wide; and if that spirit goes not forth in life, it is condemned to do so after death. (Stave 1, p. 14).
Marley’s ghost tells Scrooge that if a person does not help his fellow man while he is alive, he is “doomed to wander through the world” and witness what he “cannot share” but could have when he was alive, if he had lived a better life.
The three middle staves focus on the three ghosts of Christmas Past, Present, and Yet to Come. With each ghost, Scrooge moves closer and closer to understanding what has been wrong with his life, and how he can change it. By the time he realizes that last ghost has shown him that no one cared that he died, he is ready to change.
“Men's courses will foreshadow certain ends, to which, if persevered in, they must lead,” said Scrooge. “But if the courses be departed from, the ends will change. Say it is thus with what you show me!” (Stave 4, p. 50)
Scrooge has finally realized that he has people in his life who care about him, including his clerk Bob and his nephew Fred. He sees what he could enjoy if he spent time with them.
Stave 5, the shortest of the staves, is about Scrooge’s transformation. He has been reclaimed, and is now happy.
[It] was always said of him, that he knew how to keep Christmas well, if any man alive possessed the knowledge. May that be truly said of us, and all of us! (Stave 5, p. 56)
Scrooge transforms himself in five short chapters, and one short song. Dickens is demonstrating that it does not take much, or take long, to become a better person. All it takes is some reflection.