Scrooge did not believe in the spirit of christmas past.the spirit is visiting scrooge because before he was a man that hated christmas and did not care for anyone but himself.
The spirit took scrooge to show him that Tiny tim, the son of bob cratchit's who work for scrooge. Tim is crippled. Tiny tim died. scrooge did not want that and after that scrooge changed his ways and started give money to people in need.
scrooge is donating money to Bob and his family . after he found out that Tiny Tim was not dead he got in a happen mode and started having a christmas spirit.