Fezziwig and Scrooge are complete opposites as bosses. Scrooge is a miserly, misanthropic loner, described as follows:
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.
We learn that his clerk, Bob Cratchit, literally has a small fire, perhaps of one coal, and doesn't dare ask for more because he knows Scrooge will threaten to fire him if he does. Cratchit huddles in his comforter and tries to warm himself with his candle. Scrooge even begrudges him the day off for Christmas, saying that because he has to pay him for it anyway, it is a way of picking his pocket. Scrooge gives no Christmas party or Christmas treat. He doesn't even offer well wishes to Cratchit.
In constrast, when the Ghost of Christmas Past transports Scrooge back in time, Scrooge witnesses the joyful Christmas merriment Fezziwig has arranged. Fezziwig invites all his employees to a Christmas dance, replete with food, drink, warmth, and cheerful spirits. He is a generous, thoughtful, outgoing soul who takes time to consider the needs of others. As Scrooge ruminates, unwittingly condemning himself:
He [Fezziwig] 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.
As Scrooge is reintroduced to his past, the contrast between his own behavior to his clerk and Fezziwig's to his employees becomes painfully obvious.