Emma’s eyes were instantly withdrawn; and she sat silently meditating, in a fixed attitude, for a few minutes. A few minutes were sufficient for making her acquainted with her own heart. A mind like hers, once opening to suspicion, made rapid progress; she touched, she admitted, she acknowledged the whole truth. Why was it so much worse that Harriet should be in love with Mr. Knightley than with Frank Churchill? Why was the evil so dreadfully increased by Harriet’s having some hope of a return? It darted through her with the speed of an arrow that Mr. Knightley must marry no one but herself!
– Jane Austen
Emma, Chapter 47. Here we have Emma’s awakening when she makes the surprising discovery that she is in love with Mr. Knightley. While she spends most of the story focused on matchmaking for other people, she is remarkably blind to her own desires and romantic feelings. It takes her friend Harriet’s declaration that she has feelings for Mr. Knightley and had hopes to him returning the affection to awaken Emma’s jealousy. It makes Emma realize that Mr. Knightley should marry no one but her. The sheer force and speed of the realization of her feelings for him is emphasized by the hyperbolic metaphor, “It darted through her with the speed of an arrow.” This major turning point in the story is an important moment in Emma’s journey of self-knowledge and growth as a person.