There is an entire second novel’s worth of story implied in those seven words.
Some adaptations and reimaginings have played with the idea that Marley can save his own soul, contingent on Scrooge’s. But the Dickens text suggests nothing of the sort. So we’re left to conclude that this shade, trapped in eternal torment and regret, summoned the willpower and presence of mind to accomplish whatever afterlife hustling was necessary to make this whole plot happen, purely so his friend wouldn’t suffer the same fate.
(Old Man Yaoi Squad; I have your next assignment.)
