I like this question very much, as it is actually an excellent way of thinking about this novel. In many ways, this story focuses on the development of th ecentral character, as she moves from "having rather too much her own way, and a disposition to think a little too well of herself" to much greater humility and emotional maturity.
Emma has to learn a number of things about herself in the novel in order to make her worthy to marry Mr. Knightley, and we can see her marriage to Knightley at the end of the novel as a symbol of her reaching a level of emotional maturity that her meddling in the affairs of others during the course of the novel clearly does not indicate. If we had to sum up those lessons in one sentence, however, it would be that she must learn she is not always right and that actually she makes many mistakes, hurting others as a result of her interference. We can see this in the way that she tries to prevent Harriet from marrying the man that she truly loves in the hope of netting Mr. Elton--a man who is out of her class and is more superficial than sincer. In addition, note the way that she cruelly insults Miss Bates. Emma is forced to realise that her arrogance and belief in her own abilities are extremely misplaced and she is better off trusting the superior judgement and wisdom of Mr. Knightley.