This is how the novel starts. We find out that Marley was Scrooge's businesspartner in the introduction
Marley is a very important character as he goes to Scrooge to warn him what may happen to Scrooge in the future if he doesn't change his ways
"not a knocker, but Marley's face."
This is when supernatural events start. Marley's face shows on Scrooge's knocker and Scrooge gets scared. This is where Marley will appear to Scrooge soon
Marley regrets his actions. Him and other ghosts like him are now warning people who are like Scrooge to change their ways
"You will be haunted...by Three Spirits."
Marley is warning Scrooge that three spirits are going to visit him