Let's see. Dicken's may have written this novella to ensure that the Christmas holiday didn't fade away as it was during the Victorian era. He may have written it as an outrage against the hundreds of thousands who were suffering from the lack of common necessities, or he may have written it to warn against the abuse of children which we see with the Ghost of Christmas Present. He may have written it to warn the reader against becoming like Scrooge and the evils of greed. He may have written it to show us the true meaning of Christmas which we see in Fred and his speech and with the Cratchit family, and he may have written it emphasize the family. He may have written it to reveal the evils of the aristocratic hypocrites who turned their backs on the poor.
I would think that the message has to do with redemption being possible to change one's life. As each spirit revealed, there was a reason for Scrooge's negative reaction to Christmas and its message of giving. The bitter old man was formed by things that occurred in his past-being left alone at Christmas in a boarding school, the death of his sister, the rejection of his fiance. Christmas Past also reminded him of some of the good times (Fezziwig's party, friendship) he had that had slipped into the recesses of his mind. The negative pushed to the fore especially as a result of his business dealings. When Christmas Future showed him a lonely death with only his negativities being remembered and hinting at the death of Tiny Tim, the spirit reminds him that the future is not predetermined. Upon awakening, Scrooge sets out to redeem himself and hopefully keep Tiny Tim from an early death.