A Christmas Carol, of course, is a bit of a horror story, albeit one with a moral and an exceedingly happy ending. From the beginning of Charles Dickens' classic, it is established that the character of Ebenezer Scrooge is a miserly, bitter old man whose sole function in life appears to be the generation of revenue, usually at the expense of those less fortunate than himself. It is, however, that very sour demeanor that propels the story's narrative and that prompts the visits by four ghosts, beginning with that of his late business partner Jacob Marley. We are, however, getting ahead of ourselves. The opening pages of Dickens' story establish the fact that Scrooge is not a very nice man, and that his bitterness and outlook have adversely affected the lives of those upon whom he actually depends, primarily the Cratchit family.
Dickens, having established a general atmosphere in which his story will take place, then depicts the figure of Scrooge making his seemingly routine trip from office to home, and not just any home, but the one previously occupied by Jacob Marley. Dickens establishes mood particularly well with the following brief description of the environment to which Scrooge has returned:
"The yard was so dark that even Scrooge, who knew its every stone, was fain to grope with his hands. The fog and frost so hung about the black old gateway of the house . . ."
So, we know that Scrooge is a bitter, angry, miserly fellow. We also now know that he resides in a rather foreboding home, one that was once owned by his former business partner. As Dickens' protagonist approaches the front door of his home, the author draws the readers attention to the knocker, noting that it is anything but extraordinary -- just a plain old door knocker that happens to "very large," and that Scrooge had never had reason to pay it any particular attention. Scrooge approaches the door to the home he occupies, that was once owned by Jacob Marley. Here is how Dickens describes the scene:
"Let it also be borne in mind that Scrooge had not bestowed one thought on Marley, since his last mention of his seven-years’ dead partner that afternoon. And then let any man explain to me, if he can, how it happened that Scrooge, having his key in the lock of the door, saw in the knocker, without its undergoing any intermediate process of change—not a knocker, but Marley’s face."
The appearance of Marley's face in the large door knocker is, then, a premonition of what is to come. We do not know that the ghost of Jacob Marley will visit Scrooge that night, and warn of the imminent arrival of three spirits representing Christmases past, present, and future. The image, however, is foreboding, and initially unnerving. That Scrooge soon forgets about the image, however, is indicative of his inability to feel anything but anger and greed. The answer to the question, however -- what does the appearance of Marley's face in the door knocker symbolize -- is that the image symbolizes a life lived poorly despite the financial remunerations it has reaped, and that Scrooge will, as will be revealed about his deceased business partner, be doomed to carry in death the chains he forged in life.