The cold, lonely, friendless life of Ebenezer Scrooge stands in stark contrast (juxtaposition) against the warm, loving worlds of the Cratchit family and his nephew, Fred.
Ebenezer has the chance to have a wife and to build a life with her when he is a younger man. Instead, he chooses his greed. Belle refuses to marry Ebenezer when she realizes that his money is more important to him than she is. This leaves him alone and he becomes more and more isolated.
In his old age, Ebenezer is wealthy and lives alone with no close family or friends. When the Ghost of Christmas Present shows him the Cratchit family sharing their meager meal, he sees their love, warmth, and togetherness. He also views his nephew, Fred, who has a loving wife and is surrounded by friends at Christmastime.