What was the main reason Marley's ghost visited Scrooge?

Marley visits Scrooge to warn and show him what will happen if he does not change his life. Marley also announces the upcoming arrival of visitors..... the Spirits.

Marley comes to Scrooge to warn him that he is needed to change. He warns him that bad times will happen if Scrooge doesn't change. The Spirits will also come later to meet Scrooge.