There are a number of very important moral messages that one can take from A Christmas Carol, but arguably the most important is that money doesn't automatically bring you happiness.
The truth of this moral is illustrated by the respective examples of Ebenezer Scrooge and the family of his put-upon employee Bob Cratchit. Scrooge is a fantastically wealthy man, a self-made man whose riches are the result of years of phenomenally hard work.
And yet, despite his vast wealth, Scrooge isn't happy; far from it. Here is a man who leads a thoroughly miserable life, characterized as it is by chronic loneliness. Scrooge is such an incorrigible skinflint, such a heartless, unfeeling miser, that he has no friends and, by extension, no love or warmth in his life. Indeed, he's even so stingy that he refuses to splash out on a nice house; instead, he's content to live in a “gloomy suite of rooms” in chambers that once belonged to his business partner.
Contrast Scrooge's life with the Cratchits'. The Cratchits are dirt poor, thanks in no small part to the head of the house, Bob, being chronically underpaid by old Ebenezer. To make matters worse, they have a seriously disabled son, Tiny Tim, whose condition doesn't seem to be improving.
Even so, the Cratchit household is full of love and warmth, the very things notably missing from Scrooge's life. And despite not having much money, the Cratchits are still determined to celebrate Christmas. They'd have every reason to proclaim "Humbug!" at the very mention of the word "Christmas," but unlike Scrooge, who does utter that expression with tiresome regularity, they understand the true meaning of this most special of celebrations.