He thought it was another ghost but it wasn't.

Because scrooge needed to know that if he was to ignorant and always wanted what he didn't need he end up in a bad place all alone.

so he could feel good again about his self.

He heard the hearty laugh of the 3rd spirit.

scrooge wanted the ghost to let him say something to bells husband.He wanted him to do that so he could prove a point.

He said that he was marley the ghost.

He thought that the clock may have broke.