In Staves 1 through 3, Scrooge has seen the ghost of his former partner, Jacob Marley and has been taken around by the Ghost of Christmas Past and the Ghost of Christmas Present. Now, in Stave 4, he will be taken around by the Ghost of Christmas Yet to Come.
This ghost takes him forward in time to his own death. He finds that no one is mourning for him. He asks to be taken to see someone who is mourning and he is brought to the Cratchit house. But they are mourning the death of Tiny Tim.
After this vision, Scrooge will reform in hopes of avoiding this fate.