Jane Austen was a grand master of the devastating turn of phrase. (Casting directors for her biopic would do well to look to Janeane Garofalo or Ellen Page.) Her calling card is subtlety – she doesn't bash you over the head with her jokes, but rather slips them in so that they sneak up on you when you least expect it.
Here's a couple of examples:
But he [Mr. Elliot] had, as by the accustomary intervention of kind friends, they [Sir Walter and Elizabeth] had been informed, spoken most disrespectfully of them all, most slightingly and contemptuously of the very blood he belonged to, and the honours which were hereafter to be his own. (1.18)
The sentence starts out with a reference to "kind friends," who should do kind things, right? Well, not so much. These "kind friends" are more interested in spreading gossip and stirring up drama. By calling them "kind," the sentence sets up expectations for their behavior and then surprises you by going in an entirely different direction.
"Very well," said Elizabeth, "I have nothing to send but my love. Oh! you may as well take back that tiresome book she would lend me, and pretend I have read it through. I really cannot be plaguing myself for ever with all the new poems and states of the nation that come out. Lady Russell quite bores one with her new publications. You need not tell her so, but I thought her dress hideous the other night. I used to think she had some taste in dress, but I was ashamed of her at the concert. Something so formal and arrangé in her air! and she sits so upright! My best love, of course." (22.16)
Elizabeth's zigzags between politeness and snark are enough to give a reader whiplash. Her insistence that Anne send her "best love" to Lady Russell, sandwiched around a passage in which she tears the woman to shreds, draws a sharp contrast between Elizabeth's show of politeness and her innate selfishness.
By taking these unexpected turns, the novel's style sets up expectations only to knock them down – highlighting that appearances are never to be entirely trusted.