The Cratchits provide a counterpoint to Scrooge and illustrate the novel's predominate theme: that family and generosity are more valuable than great riches. Scrooge has the one thing they don't, money, but Cratchits have everything else that leads to happiness and contentment: family, love, kindness and generosity.
While Scrooge sits alone amid his piles of money in his dark, gloomy house, hoping the poor will die and rid the world of excess population, poor sick Tiny Tim, the youngest Cratchit, who is doomed to die if his family doesn't find more money, blesses everyone. Likewise, Bob Cratchit, the clerk Scrooge underpays and overworks, remains cheerful because he has what matters most in life: a loving family and a good heart.
Dickens' believed that transforming and softening the hearts of individuals would reform capitalism without any need of a revolution. A Christmas Carol strongly articulates that theme. Scrooge may smart about making money, and Bob Cratchit ignorant on that front, but in the end, it's social intelligence, the ability to get along with and enter into good-hearted relationships, that matters. In the book, Scrooge, who has grown ignorant of the importance of community, takes an unwanted journey that leads him to become more like the Cratchits, who, in the end, possess life's real riches. And as Scrooge becomes more like them, he shares with them the one thing they need (and Dickens never lost sight of the fact that the poor needed money), some small portion of his wealth.