Elizabeth sends home a note requesting that her mother come and visit Jane. Mrs. Bennet arrives with Lydia and, not wishing Jane to leave Bingley's company, declares that Jane seems worse than ever.
Mrs. Bennet continues her ridiculous and manipulative campaign to "win" Bingley for Jane.
In conversation, Mrs. Bennet, seeking to raise Jane's status, tries to impress Bingley about her family and their situation in the country. Darcy suggests that one finds more variety of character in town than in the country, but Mrs. Bennet loudly objects. Everyone is surprised. Elizabeth is mortified and tries her best to fill the awkward silence.
By talking up the Bennets' status, Mrs. Bennet actually degrades it by seeming crass, foolishly proud, and clearly not of the best class or character. If you're high class, you don't need to tell others about it—they just know.
Lydia jumps in to remind Bingley of his promise to give a ball at Netherfield. Bingley says he hasn't forgotten but will wait until Jane recovers.
Lydia's insistence is impolite. Bingley, with his better breeding, turns it into a compliment to Jane.