A Christmas Carol is quite allegorical, as it features events and characters with clear symbolic meaning. For instance, Scrooge represents greed and selfishness. Bob Cratchit represents common humanity. Tiny Tim represents the disadvantaged members of society. Each ghost stands for a stage of Scrooge's life.
Perhaps the most striking allegorical figures are the children who cling to the Ghost of Christmas Present (who represent Ignorance and Want):
From the foldings of its robe, it brought two children; wretched, abject, frightful, hideous, miserable[...]. Where graceful youth should have filled their features out, and touched them with its freshest tints, a stale and shrivelled hand, like that of age, had pinched and twisted them, and pulled them into shreds.
Strings of negative adjectives make up the portrait of these two miserable children. Although Marley's ghost terrified Scrooge, it did not have as much impact on him as these frightful children. In a way, they represent Scrooge's most detestable qualities. They also suggest that his greed breeds ignorance and want among the poor people whom he refuses to help.
The general message of A Christmas Carol is that it's never too late to change your character for the better. It might take a lot of terrifying soul-searching, but it will result in a long and happy life.