The funny and sarcastic narration of Emma—combined with all the ironic moments where Emma’s assumptions and matchmaking impulses are incorrect—contributes to a funny, light-hearted mood for most of the novel.
The mood becomes heavier in critical moments, such as when Knightley criticizes Emma for insulting Miss Bates or when Emma has to tell Harriet that Mr. Elton is interested in her and not Harriet. The climax of the story—when Emma realizes that she loves Knightley—is perhaps the best example of a mood shift, as Emma has just gone from gossiping with Harriet to reckoning with her long-repressed feelings for her life-long friend:
Till now that she was threatened with its loss, Emma had never known how much of her happiness depended on being first with Mr. Knightley, first in interest and affection.—Satisfied that it was so, and feeling it her due, she had enjoyed it without reflection; and only in the dread of being supplanted, found how inexpressibly important it had been.
Though Emma has reflected on her behavior in more serious terms before, she has not yet reckoned with her own romantic feelings. In fact, the entire novel rests on Emma’s absolute clarity that she will never get married—this is what propels her to become a matchmaker who meddles in others’ affairs. This moment therefore shifts the mood into an entirely new, romantic register as Emma accepts that she, too, longs for love and wants to come “first” to Knightley as well.
After this moment, the mood the novel becomes more earnest and, after Knightley reveals that he loves Emma in return, shifts into a more grounded and peaceful state. The novel ends with three happily-ever-afters (Emma and Knightley, Jane and Frank, Harriet and Mr. Martin), leaving readers feeling settled and content.