From our 21st century perspective, the concerns of Pride and Prejudice might seem trivial. Who cares if the Bennet girls ever get married? Can't they just go on living their fabulous single lives as unaccountably wealthy journalists or gallery owners?
Well, no. In the early nineteenth century (and in most parts of most centuries in most parts of the world), marriage was the only option for respectable young women. There was no such thing as moving out of your parents' house, no such thing as building a career in your twenties and worrying about marriage later, and (importantly) no such thing as divorce, except in really extreme, unusual circumstances. (How extreme? Divorce required an act of Parliament—like having the Senate vote on whether or not you could break up.) Marriage was literally the most important decision a woman could make. It could ruin you (Lydia, Mrs. Bennet); set you up for life (Jane, Lizzy); or condemn you to a mediocre but independent existence (Charlotte). It's like a Choose Your Own Adventure book, except you might accidentally end up with Mr. Collins instead of falling into a pit full of venomous vipers.
Pride and Prejudice argues against the idea of love at first sight and suggests that the better kind of love develops slowly.
Although both Jane and Elizabeth have happy marriages, the narrator approves more of Elizabeth's.