Letters are often used to explain people’s true roles in events that have happened in the past, such as Darcy’s role in the whole Wickham situation. Austen uses these letters in order to let the reader and the character to whom the letter is addressed find out the letter writer’s true intentions. Letters also are used to say things that the characters are sometimes too proud to say, for instance when Darcy writes the letter to Elizabeth explaining the truth of his actions, after she’s accused him of things and wounded his pride.
The letters in "Pride and Predudice" help communicate important information and allow Austen to quickly communicate information that would have taken much longer if written in narrative form. In fact, one is a turning point in the novel. After Jane refuses Darcy’s first marriage proposal, he delivers a letter to her. After reading the letter, she realizes that she placed her trust in Wickham's good looks and easy sociability, forgetting completely about the impropriety of his disclosures and actions. A gentleman would never reveal the negative kind of information he told Elizabeth about Darcy to a stranger, as Elizabeth was to him. She is mortified that Wickham's attentions blinded her to his faults. Other letters, such as the one Jane receives from Miss Bingley and Elizabeth receives from her aunt, have much the same function. They allow the narrative to intensify quickly without spending many pages describing the events. In addition, they allow changes in character's views of one another and help the reader understand the motivations behind many of the characters' actions.
Letters play a very important role in the novel. The two main purposes which they fulfil are 1. To reveal the character and personality of the letter writer and 2. To convey information.
A good example of a letter which primarily conveys important information is Mrs. Gardiner's letter in Ch.52, which reveals the fact that it was Darcy who was responsible for compelling Wickham to marry Lydia.
A letter which is meant to primarily reveal the personality of a character is Collins' letter in Ch.13. After reading his letter Mr. Bennet and Elizabeth correctly judge Collins' character, "Can he be a sensible man sir?" "No my dear; I think not."
A letter which combines both these functions simultaneously is Darcy's letter in Ch.35. The letter contains the important revelation of Wickham's villainy in trying to elope with Darcy's sister; at the same time it also reveals the inherent pride of Darcy: "I write without any intention paining you or humbling myself."
Some letters are printed complete with the dates, like Collins' and Mrs.Gardiner's for instance. This is because Jane Austen wishes to remind her readers of the passage of time in the novel. In contrast some letters are discussed by two characters to create an impression of drama. In Ch.21 Jane and Elizabeth discuss Caroline's letter which creates an intensely dramatic scene because they are worried that Bingley might not return to Netherfield at all.