Contrast is the most important literary device in the novel. It is more important than comedy, sentiment, and nightmare because it includes each of these modes. We have seen how Dickens plays each of these methods against the others in a complementary way.
Dickens defines his characters through dramatic contrasts, by having them collide. In the collisions they reveal their essence. Mr. Pickwick stands at the center of the novel in a moral sense: everyone else is measured against him. Through these multiple contrasts we get a fully developed portrait of Mr. Pickwick: his attitudes toward women, friends, scoundrels, defeated enemies, mercenary marriages, disinterested love, travel, liquor, good food, and pretense.
The result of Dickens' thoroughgoing use of contrast was to develop a method for exploring his themes, a method he would use in novel after novel with increasing success. By using characters to reflect various facets of an idea, Dickens found he could develop his fictional ideas in depth. This method is analogical; it creates a fictional world that is coherent because it is based on some central idea or metaphor. Shakespeare and Tolstoy also used this method extensively.
Dickens took this basic relationship and developed it into a moral spectrum ranging from the near-perfect Pickwick to the bestial characters of the interpolated tales — from the good Sam Weller to the dissipated Bob Sawyer and Ben Allen. Mr. Pickwick and Sam Weller would lack definition if they had not been tested against these other types. No matter how outrageous Dickens may be in his caricatures, he has developed a very sound method for giving his novels reality, subtlety, and depth.