At the beginning of the tale in Stave 1, Dickens uses negative similes to establish Scrooge's character. Apparently, Scrooge is:
Hard and sharp as flint, from which no steel had ever struck out generous fire; secret, and self-contained, and solitary as an oyster.
Flint and oysters are not very palatable things to be compared to. Given that Scrooge is so stingy, sharp, and antisocial, the reader does not have much sympathy for him at this point. However, at the end of the tale in Stave 5, Scrooge employs a string of similes to celebrate his return to the present:
I am light as a feather, I am as happy as an angel, I am as merry as a school-boy. I am as giddy as a drunken man.
This self-description provides evidence of his transformation. It contrasts sharply with the narrator's initial description, as these positive similes differ greatly from ones like "as hard and sharp as flint" or "solitary as an oyster." Indeed, Scrooge has become a new man. Instead of being hard and sharp, he is soft and light. Instead of being a crotchety old man, he feels like a schoolboy. He becomes nearly inebriated with joy.
When Scrooge finds himself able to embrace his community, he finds himself forever changed. Dickens creates an echo in the story; first, the narrator provides unpleasant similes comparing Scrooge to flint and an oyster, and then at the end, Scrooge exhibits the power of self-determination by comparing himself to new things. This might seem like a small detail, but regardless of whether or not the reader consciously juxtaposes these similes, they underscore Scrooge's transformation and provide evidence of a true change of heart.
The most famous simile in A Christmas Carol (and arguably one of the most famous similes in literature overall) appears on the very first page:
Old Marley was as dead as a door-nail.
The narrator repeats this line in the next paragraph to emphasize that Marley is, indeed, dead. Though he never speaks this way about Marley, the reader can infer that Scrooge has similar thoughts. A doornail is notably small and insignificant, but it can be used to build things. This idea recalls Marley's role as a sort of tool in Scrooge's business. Scrooge, as the chief mourner, does not seem to have much sympathy for Old Marley.
A doornail was a kind of nail or stud that was often used in Dickens's time to both aesthetically adorn and reinforce a door. Generally speaking, nails can usually be used more than once. But in Dickens's era, it was customary to hammer doornails into doors in such a way that made them useless for anything else. If the nails were hammered so their tips extended to the other side of the door, and then hammered flat against that side, they could not be extracted. Perhaps this is why Dickens chose to compare Marley to a doornail—a flattened doornail and a corpse are both fairly useless, with little to no chance of serving a purpose ever again. And yet, though the removal of such doornails is difficult, it is not impossible, and this slyly hints at the return of Marley's ghost.
The simile first appeared in Shakespeare's Henry IV. When Jack Cade leads a rebellion against the king, he declares that "if I do not leave you all as dead as a doornail, I pray God I may never eat grass more." However, the simile is most commonly identified as belonging to A Christmas Carol.
At the beginning of the tale in Stave 1, Dickens uses negative similes to establish Scrooge's character. Apparently, Scrooge is:
Hard and sharp as flint, from which no steel had ever struck out generous fire; secret, and self-contained, and solitary as an oyster.
Flint and oysters are not very palatable things to be compared to. Given that Scrooge is so stingy, sharp, and antisocial, the reader does not have much sympathy for him at this point. However, at the end of the tale in Stave 5, Scrooge employs a string of similes to celebrate his return to the present:
I am light as a feather, I am as happy as an angel, I am as merry as a school-boy. I am as giddy as a drunken man.
This self-description provides evidence of his transformation. It contrasts sharply with the narrator's initial description, as these positive similes differ greatly from ones like "as hard and sharp as flint" or "solitary as an oyster." Indeed, Scrooge has become a new man. Instead of being hard and sharp, he is soft and light. Instead of being a crotchety old man, he feels like a schoolboy. He becomes nearly inebriated with joy.
When Scrooge finds himself able to embrace his community, he finds himself forever changed. Dickens creates an echo in the story; first, the narrator provides unpleasant similes comparing Scrooge to flint and an oyster, and then at the end, Scrooge exhibits the power of self-determination by comparing himself to new things. This might seem like a small detail, but regardless of whether or not the reader consciously juxtaposes these similes, they underscore Scrooge's transformation and provide evidence of a true change of heart.