Marley's ghost goes to Scrooge to warn him that if he continues to act the way he does and treat others poorly that he'll be punished for his sins in the afterlife. This scares Scrooge, but he doesn't entirely believe it until later on in the play; however, it sets up the journey Scrooge goes on throughout the rest of the play. I don't know if that's the kind of answer you were looking for, but I tried.
