Please compare the events that take place in Stave Two, in the warehouse, to the events of Stave One, in Scrooge's counting-house.
Second scene shows Scrooge at a warehouse where he serves as a young apprentice. Compare this to the old Scrooge in his counting-house in A Christmas Carol.
First, let's begin with opening description of Scrooge as he is in Stave One:
Oh! but he was a tight-fisted hand at the grindstone, Scrooge! a squeezing, wrenching, grasping, scraping, clutching, covetous old sinner! Hard and sharp as flint, from which no steel had ever struck out generous fire; secret, and self-contained, and solitary as an oyster.
So, before we see the young man he was, as shown to him by the Ghost of Christmas Past in Stave Two, we see the shrivelled, "tight-fisted," miser that he has grown to be. In his counting house, he does not let Cratchitt add coal to the fire, spurns his nephew's invitation to join him on Christmas day, refuses to give some of his great wealth to charity to help the poor. He says:
Are there no prisons?. . .And the workhouses?. . .Are they still in operation?. . .I don't make merry myself at Christmas, and I can't afford to make idle people merry. I help to support the establishments I have mentioned: they cost enough: and those who are badly off must go there.
And he ends the scene begrudgingly allowing his employee to take Christmas day off, telling him to be in "all the earlier the next morning."
This is in huge contrast to Fezziwig's warehouse in Stave Two. Fezziwig himself is jolly and approachable, and Scrooge and his companion Dick work happily for him. In contrast, to Scrooge's cold, miserable counting house, here is how Dickens describes the warehouse:
[T]he floor was swept and watered, the lamps were trimmed, fuel was heaped upon the fire; and the warehouse was. . .snug, and warm, and dry.
There were. . .dances, and there were forfeits, and more dances, and there was cake. . .and there was a great piece of Cold Roast, and there was a great piece of Cold Boiled, and there were mince-pies, and plenty of beer.
In short, Fezziwig is throwing an all-out "office" Christmas party, with Scrooge out amongst the crowd, making merry, dancing, eating and drinking with his fellows. Quite the contrast to the sort of employer that Scrooge has proved to be in his later years at his own counting house.
The Ghost and Scrooge then discuss the sort of employer that Fezziwig was:
“A small matter,” said the Ghost, “to make these silly folks so full of gratitude.”
“Small!” echoed Scrooge.. . .
“Why! Is it not? He has spent but a few pounds of your mortal money: three or four perhaps. Is that so much that he deserves this praise?”
“It isn't that, Spirit. He has the power to render us happy or unhappy; to make our service light or burdensome; a pleasure or a toil. Say that his power lies in words and looks; in things so slight and insignificant that it is impossible to add and count ’em up: what then? The happiness he gives is quite as great as if it cost a fortune.”
And with these words, Scrooge has made his first step towards transformation. He realizes, in comparing himself to Fezziwig, that he isn't the sort of employer he would like to be at all!