The reader finds out through Scrooge's visits to Christmases past that Scrooge was a very lonely little boy who wasn't shown much love. He is alone most days at school, although there are certain characters who do show him affection, kindness, and acceptance--the characters he imagines out of Ali Baba and Robinson Crusoe as well as his little sister, Fan, and his former employer, Mr. Fezziwig. Through these memories, Scrooge realizes that it takes very little money to make others happy--the parties that Fezziwig threw for his employees is the perfect example of this--and we see the icy shell of Scrooge beginning to melt.
The visits to Christmases present and future focus on Tiny Tim and his disease and the death of Scrooge himself, which no one really mourns. The small and emaciated figure of Tiny Tim touches Scrooge in such a way that he inwardly vows to do something about it...in his change of character and outward show of feeling toward his fellow man--the boy who gets money to buy the biggest turkey, the Christmas dinner for the Cratchit family, and Scrooge's attendance at his nephew's dinner party--ensures that he will be a man whose death is mourned and who will be missed more than just someone whose bed curtains are torn down and whose clothes are collected and sold by the servants of the house.
Scrooge's past is not one to be proud of...if his change is genuine, he deserves a second chance and forgiveness.