Fezziwig symbolizes all the good that a human can possess, particularly a human who is a business owner. When Scrooge revisits his past, he is reminded of what a boss can and should be. He treats both Ebenezer Scrooge and Dick Wilkins wonderfully, telling them "No more work to-night," in direct contrast with Scrooge's constant effort to work every last second out of his own employee, Bob Cratchit. He throws a wonderful party, and is himself the epicenter of the joy and energy of it. During the dances, Old Fezziwig and his wife are more than a match for all the other, younger dancers. Dickens writes
A positive light appeared to issue from Fezziwig's calves. They shone in every part of the dance like moons. You couldn't have predicted, at any given time, what would become of them next.
Dickens as already established a strong correlation between goodness and light, but here he gives us a human character who seemingly radiates goodness so much goodness that it is almost literally manifests itself.
As the party goes on, and Scrooge finds himself absorbed in the light and joy that is Fezziwig, the Ghost of Christmas Past baits Scrooge slightly, wondering why people care so much for Fezziwig when the man hasn't spent that much money "to make these silly folks so full of gratitude." Here Scrooge replies
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.
Through manner and deeds, Old Fezziwig symbolizes all that is charitable and good within humankind, and he serves as not only a mentor in Scrooge's past, but a guide for Scrooge's future.