Mr. Collins gloats as they prepare for the dinner. He condescendingly tells Elizabeth not to worry that her best dress is simple, because Lady Catherine "likes to have the distinction of rank preserved."
Class rank is not about personal substance: it is all about the outward and arbitrary.
At Rosings, they meet the haughty Lady Catherine, whose conversation consists entirely of commands and strong opinions. Mr. Collins and Sir William Lucas suck up to her, agreeing with everything she says. Miss De Bourgh is uncommunicative and dull.
After lecturing Charlotte about how to run her household, Lady Catherine asks Elizabeth a series of invasive questions about her family, property, and upbringing. She disapproves of the Bennets' choices—educating their own daughters, failing to provide musical training—and is astonished that Elizabeth answers so pointedly, offering her own opinions to counter Lady Catherine's.
Lady Catherine, like Darcy, believes in a set of "accomplishments" for women. In contrast, Elizabeth is self-made and proud of having determined her own character.