Marley, Scrooge's former partner, is the instrument of Scrooge's redemption.
Jacob Marley has died deep in the sin of indifference to the needs of others. It is a fate that is illustrated as one of aimless wandering, heavily burdened with the chains "he forged in life, link by link" through his callous, stingy, materialistic behavior.
Marley plays a central role in convincing Scrooge that he must change his life or face an eternity of suffering. It is Marley who visits Scrooge as a ghost and acts as his conscience, reminding him of all the indifference they, as business partners, showed in their efforts to grow wealthy.
Marley must convince Scrooge that there are consequences to his behavior. He tells Scrooge to expect three spirits.
Jacob Marley was Scrooge's business partner and probably his only friend in his later years. Marley's spirit is the first to visit Scrooge to warn him that he will be visited by three more spirits that night. Scrooge notices that Marley is bound by a chain and asks the spirit about it. Marley tells him that the chain is the burden he forged in life out of the "cashboxes, keys, padlocks, ledgers, deeds, and heavy purses wrought in steel"--that is, the things he cared about most in life are now a heavy burden to him in death.
Jacob Marley is Scrooge's old business partner who died. In the story, Marley returns from the dead to warn Scrooge of the visits of the three ghosts that he will encounter.
Marley was Scrooge's former buisness partner that died. He came back as a ghost to haunt him to change.