why is the epilogue necessary?

The epilogue of Crime and Punishment is generally misunderstood and criticized, but it is in fact quite necessary to the story. In the epilogue we see how Raskolnikov has journeyed from a state of Russian nihilism to a place where he has acted on his own beliefs and theories about life, only to find that he was in essence wrong. He eventually admits that a crime has in fact been committed, and that not only has he committed a crime in the eyes of others but has broken his own moral code as well. The epilogue brings this all together, and in seeing the implications of what his theory truly means, he finds redemption and begins to understand the need for spiritual healing. Besides this, the epilogue serves to apprise us of Dostoevsky's true purpose, that being to provide a warning against Russian nihilism and its attempt to remove God and morality from society.

The epilogue concludes the book by showing Raskolnikov's transformation into a human being. His alienation from society due to the murder is ended when he realizes he is not above moral law and admits his love for Sonia. Without the epilogue we would have never even known if Raskolnikov was imprisoned, thus possibly changing the theme of the book to mental punishment overruling actual punishment. The epilogue ends the theme and resolves Raskolnikov's inner struggle of his superiority.