The last scene with this ghost is with Belle where we see just how obsessed by money he has become. In the scene Scrooge observes that there is "nothing the world is so hard on as poverty." Scrooge is terrified of being poor - which is understandable given how horrendous the conditions in workhouses were. But he responds to this by becoming
obsessed by money. Belle goes on to say that "the master passion, Gain, engrosses you." Here, she is saying that gain - or greed - has taken him over. His "nobler aspirations" - the good things he once believed in - are gone, and now he simply wants money. This is so important because the Scrooge we knew at the beginning didn't care for anything but money, though here, Belle is saying that once, before all this, she fell in love with someone who loved something more.