Why is Lady Catherine important if she is mostly comic?

Lady Catherine is class ideology with a speaking part. Through her, Austen stages the marriage market’s snobbery without needing a treatise: rank should dictate marriage, talent should defer to patronage, and Elizabeth’s manners are an offense against hierarchy. The comedy of her lectures makes the power claim easier to see — and easier to refuse.

She also catalyzes the ending. By trying to bully Elizabeth out of a rumor of engagement to Darcy, she prompts the frankness that helps bring Darcy back. Functionally she connects Rosings, Collins, and Darcy’s family pride to Elizabeth’s independence. Read her not only as satire but as a node linking “social class,” “individual vs society,” and Darcy’s need to separate inherited arrogance from chosen honor.