Ebenezer Scrooge learns much from the ghost of his former partner, Jacob Marley, in A Christmas Carol by Charles Dickens. When Scrooge asks the ghost of Marley why he is there, Marley answers,
"'It is required of every man,' the Ghost returned, 'that the spirit within him should walk abroad among his fellow men, and travel far and wide; and if that spirit goes not forth in life, it is condemned to do so after death. It is doomed to wander through the world--oh, woe is me!--and witness what it cannot share, but might have shared on earth and turned to happiness.'" (Dickens 21)
Marley is warning Scrooge here that he will suffer the same fate as Marley if he continues with his selfish ways. Scrooge asks about the chain Marley wears and is told that each link in it represents all the evil Marley did during his life. He adds that Scrooge's chain will be even heavier and longer because Scrooge has continued his ways since Marley's death. Scrooge tells Marley that he was a good businessman when he was alive, as if that should count for something, but Marley replies that business was not what mattered--that humankind was, and he had failed miserably.
Jacob Marley's purpose in A Christmas Carol is to warn Scrooge of his own fate and to introduce him to the three other spirits who are about to visit him in hopes that he will choose a different fate than the one Marley has.