Tiny Tim serves a symbolic role. He puts a face to the thousands of faceless poor children Dickens saw in London every day.
Many of Dickens’s works are about poor children, but A Christmas Carol is the most powerful and the most sentimental. Dickens loved sentiment, but so did his readers. You can walk by a poor urchin on the street every day, but would you walk by Tiny Tim? Dickens hoped his readers wouldn’t.
By creating a character that was clearly a victim of his fate, and in no way responsible for it, he hoped his readers would realize what it was like to be poor, and start caring.
Alas for Tiny Tim, he bore a little crutch, and had his limbs supported by an iron frame! (Stave 3, p. 32)
Notice that Tiny Tim is the perfect religious figure. He is sacrificed to help Scrooge understand the consequences of not caring about people. Tim is crippled, and dies from lack of simple food and medical care. This is directly the result of Scrooge not paying Bob Cratchit enough, and not caring enough about his family to inquire about them. Scrooge’s ignorance about Tiny Tim is symptomatic of how out of touch he is.
Scrooge is so impressed by the boy’s piousness, and his blessing, that he asks if Tim will die. When the ghost tells him he will, he cries out in shock and asks why the boy can’t be spared.
“… What then? If he be like to die, he had better do it, and decrease the surplus population.” (Stave 3, p. 34)
Scrooge hangs his head in shame when the words he spoke to the men asking for charity for the poor are flung back at him. The ghost asks him to “forbear that wicked cant” and remember where the surplus is, reminding him that “in the sight of Heaven, you are more worthless and less fit to live than millions” (p. 34)
In the end, Dickens delights in telling us that Tiny Tim did not die, and Scrooge was like a second father to him. In the end, at least one boy was saved. Dickens hoped his readers would try to save some children themselves.