What is Jane Austen trying to say about the character and vocation of the novel through Emma, in her novel Emma?
On one level, Emma is a novel about about artistic endeavor and how we receive it. Austen lays this out in chapter 6, as Emma draws a portrait of her friend Harriet. In the comments other characters make about this portrait, we learn how the artist (or writer), either by design or lack of skill, can alter reality. Emma's portrait makes Harriet more beautiful than she really is, a move Austen critiques. Austen shows us through the action of the novel that Emma's attempt to similarly be an "artist" and alter reality leads to trouble. Were this not a comedy in the mode of A Midsummer's Night Dream, we could well imagine Emma's artistic rearrangement of life as a recipe for disaster.
In chapter 6, Mr. Knightley's criticisms of Emma's enhancements of Harriet in her portrait foreshadow the ways he will criticize her actions in real life. "'You have made her too tall, Emma' said Mr. Knightley." Emma refuses to agree, though she knows what he says is true. She will continue to try to remake life in her own image until a series of mishaps help her learn to embrace reality. Austen's makes the point, as does Flaubert in Madame Bovary or Cervantes in Don Quixote, that art (or literature) that indulges too heavily illusion can create wreckage real life.