At this point in the novella, Scrooge is a completely changed man, but Cratchit doesn't know it, so Scrooge plans on playing a joke on Cratchit. When Cratchit sneaks into the office a whole "eighteen minutes and a half" late, Scrooge growls at him in his usual manner and scolds him for being so late, and then he leaps off his stool and gives Cratchit "such a dig in the waistcoat that he staggered back into the Tank again."

At this point, just when Cratchit fears that Scrooge is going to fire him, Scrooge states "therefore I am about to raise your salary." Cratchit can't believe his own ears, for he

trembled, and got a little nearer to the ruler. He had a momentary idea of knocking Scrooge down with it; holding him; and calling to the people in the court for help and a strait-waistcoat.

What a shocking surprise Scrooge's statement is to Cratchit; he believes Scrooge has gone insane, and to further shock Cratchit, Scrooge says "A merry Christmas, Bob!" and states that he will "endeavour to assist [his] struggling family" and then he instructs him to "buy another coal-scuttle" before he gets to work.

Wow! Can you imagine what Cratchit must have been thinking.

Up until this point in the story, Scrooge has always been a really nasty boss.  But then he met Marley's ghost and the three ghosts who showed him the past, the present and the future.

So now (the morning after Christmas) Scrooge has reformed.  He has already bought the biggest turkey and had it sent to Cratchit's house.  So now Cratchit comes in late and Scrooge pretends to be really angry.  He makes Cratchit come back into the tank with him, but then he tells him (in an angry voice) that he's going to raise his salary.