Early in the novel, Emma tells Harriet about her feelings toward Jane Fairfax, using hyperbole to describe how beloved Jane is:
“Every letter from her is read forty times over; her compliments to all friends go round and round again; and if she does but send her aunt the pattern of a stomacher, or knit a pair of garters for her grandmother, one hears of nothing else for a month. I wish Jane Fairfax very well; but she tires me to death.”
This language is hyperbolic in that it is unlikely that every letter Jane sends is read a whopping 40 times, or that any small gift she sends is all her family talks about for an entire month. Still, Austen has Emma use hyperbole here to capture the intensity of Emma’s pride and vanity at the start of the story, along with her propensity to misjudge and misperceive people. Not only is Emma stretching the truth about Jane, but also about her relatives—Mrs. Bates and Miss Bates—reducing them to people who are unbearably obsessed with their daughter/niece.
Later in the novel, after growing up some, Emma is able to appreciate Jane and no longer gossips about her in this way, viewing her as a friend instead. She similarly reckons with her rudeness toward Miss Bates and makes amends.
Near the end of the novel, Emma learns that Harriet is in love with Knightley—and believes Knightley to possibly love her in return—and Emma has also realized that she is in love with Knightley. As she reacts internally to these huge reveals, Emma uses hyperbole:
With insufferable vanity had she believed herself in the secret of everybody's feelings; with unpardonable arrogance proposed to arrange everybody's destiny. She was proved to have been universally mistaken; and she had not quite done nothing—for she had done mischief. She had brought evil on Harriet, on herself, and she too much feared, on Mr. Knightley.
In using hyperbolic language—“insufferable vanity,” “unpardonable arrogance,” “she had brought evil”—Emma communicates the depth of her pain and regret. This is not a revelatory moment like when Mr. Elton declared his love for her or when Mrs. Weston told her of Frank’s secret engagement to Jane. As the climax of the novel, this moment is bigger and more painful (and thus requiring hyperbole), because Emma is finally fully reckoning with her pride and vanity and maturing into the more grounded person and mature person she becomes by the end of the book.
When Emma learns that Knightley is in love with her and not Harriet (as she had previously assumed), she uses hyperbolic language in her internal thoughts:
While he spoke, Emma’s mind was most busy, and, with all the wonderful velocity of thought, had been able—and yet without losing a word—to catch and comprehend the exact truth of the whole; to see that Harriet’s hopes had been entirely groundless, a mistake, a delusion, as complete a delusion as any of her own—that Harriet was nothing; that she was every thing herself.
Emma’s declaration “that Harriet was nothing; and she was every thing herself” could be interpreted as a slight toward her friend, but it is more than that. Emma does not actually believe Harriet to be “nothing,” as in devoid of value as a person. She has simply realized that, in Knightley’s mind, Emma is the object of his romantic affections and Harriet is but a friend.
The language she uses harkens back to a declaration of hers that came earlier in the novel—that she did not want to marry because she could not imagine coming “always first and always right in any man’s eyes as I am in my father’s.” The hyperbole here captures how wrong she was and how delighted she is to realize she now comes first to Knightley. Ultimately, Emma’s extreme reaction here shows both the depth of her love for Knightley as well as the depth of her misperceptions about Knightley, Harriet, and herself.