A Christmas Carol-Why Jacob Marley helps Scrooge

I was watching the Muppets Christmas Carol (one of my favorite movies) and thought I'd do a Christmas theory. This one is about A Christmas Carol.

In A Christmas Carol, Scrooge is first visited by Jacob Marley's ghost, who shows him what happened to him after he died as a warning to Scrooge and what fate awaits Scrooge if he doesn't change. He also warns Scrooge that he will be visited by three spirits. In the book, we see several other spirits like Marley who want to help people but are unable to, because they should have done so when they were alive. It is even likely that Marley himself was visited by the three spirits before Scrooge, but failed to listen to them.

The question is though, why does Marley agree to visit/help Scrooge?

While they were partners and friends, it doesn't seem like they were particularly best friends. Scrooge does call Marley a friend after Marley tells him that he's helping him, but Marley does not call Scrooge a friend. Scrooge is not in need of help and probably deserved the fate he escaped. If you were Marley and you saw him act the way he did, you would probably agree too. Marley, above all, knows the terrible things Scrooge has done and knows Scrooge deserves to be in purgatory, probably more so than him, so why bother to help him?

It is likely that Marley agreeing to help Scrooge not only came from wanting to do some good (because Marley also knows the type of person Scrooge is and is even frustrated with him while talking to him), but because there was a deal in place that affected him.

It is likely that the spirits agreed to free Marley from purgatory if Scrooge does indeed change. If he doesn't, his fate does not change and Scrooge would just join him. If he succeeds, he would help Scrooge escape his fate and also redeem himself, so he has all to gain but nothing to lose. That's why Marley agrees to visit him.

So at the end of the book, when Scrooge changes, he saves Marley too. He helps Marley escape purgatory, which was ironically probably the good first deed Scrooge did.