Why do you think the image of Marley appears to Scrooge?

Marley was Scrooge's only friend and partner. Only Marley's warning could stir Scrooge and prepare him for the events that would follow. Seeing Marley in his imprisonment and hearing warnings from the one man he associated with in life create as realism that draws the reader into the story and makes it believable..... as unbelievable as it may seem.