What is the lesson scrooge learns in this stave that he had not learned before? why is this stave needed when scrooge's attitude has already changed so much?

In Stave 4, Scrooge learns the truth about the value of his life as it applies to other people.  What he comes to see through the lessons of the final spirit, the Ghost of Christmas Yet To Come, is that when the final tally is taken, his life, in the eyes of his fellow man, will be worth nothing.  He has not left a lasting legacy; there will be no one to mourn his passing