In the first stave (or chapter) of A Christmas Carol, we meet Marley, Scrooge's deceased business partner, who is encased in heavy chains. These chains are made of steel and are weighed down with "cash-boxes, keys, padlocks, ledgers, deeds, and heavy purses."
Further on, we learn why Marley is forced to wear this chain in the afterlife:
"I wear the chain I forged in life," replied the Ghost. "I made it link by link, and yard by yard; I girded it on of my own free will, and of my own free will I wore it."
This chain, then, is symbolic of Marley's business affairs and his pursuit of wealth when he was alive. Like Scrooge, he focused on enriching himself instead of caring about the plight of others. As a result, he is forced to wear this chain in the afterlife to remind him of his neglect of others and to encourage redemption. This has clearly worked: Marley's conversation with Scrooge shows how his character has transformed.
The chains are also symbolic of Marley's attempt to reform Scrooge's character. It is interesting to note, for example, that Marley clanks his chains every time that Scrooge says something negative or reminds him of his previous misdeeds. For instance, when Scrooge mentions that Marley was always a good man of business, he shakes his chains in response. In this respect, the chains symbolise the beginning of Scrooge's transformation and the heavy price he will pay should he fail to see the errors of his ways.