One of the most well-known figures in all of literature, Tiny Tim is less a character and more a representation of the less fortunate, one who maintains a positive attitude and commitment to Christian ideals in spite of his dwindling health. It’s made clear that Tiny Tim is suffering because of Scrooge’s greed, illustrating a clear link between the dismissive cruelty of the upper classes embodied by Scrooge and the pitiable state of the poor, as exemplified by Tiny Tim. The two are blatant opposites; Tiny Tim appears to possess the grace and wisdom of a much older soul and finds a silver lining to his condition, expressing the wish that it will remind churchgoers of Christ and thus make for a happier holiday (a connection Dickens uses to suggest Tiny Tim is himself a Christ figure). Scrooge, in contrast, never thinks of anyone but himself.
Though the role he occupies is largely symbolic, Tiny Tim is at his most human when he, like his mother and the rest of his siblings, chooses not to toast to Scrooge. He is still, after all, a child, and no doubt fearful of “the Ogre of the family.” For his part, Scrooge is unsettled by his visit to the Cratchits with the Ghost of Christmas Present, indicating his icy heart is beginning to melt. He is unable to empathize with a nameless, faceless lower class, but to see a child such as Tiny Tim suffering, and to know he will likely die soon, gives Scrooge pause and forces him to feel connected to the fate of another human being.