Quote 1
"Indeed, Jane, you ought to believe me. No one who has ever seen you together can doubt his affection. Miss Bingley, I am sure, cannot. She is not such a simpleton. Could she have seen half as much love in Mr. Darcy for herself, she would have ordered her wedding clothes. But the case is this: We are not rich enough or grand enough for them" (21.18)
Lizzy is trying to convince Jane that Bingley really does love her, but Miss Bingley is trying to keep them apart. (Duh.) Notice Austen uses "affection" almost as a synonym for "love." We usually think of "affection" as a pretty mild emotion, but does it mean something stronger for Austen?
Quote 2
[Colonel Fitzwilliam:] "[…] But in matters of greater weight, I may suffer from want of money. Younger sons cannot marry where they like."
[Elizabeth:] "Unless where they like women of fortune, which I think they very often do."
"Our habits of expense make us too dependent, and there are not many in my rank of life who can afford to marry without some attention to money."
"Is this," thought Elizabeth, "meant for me?" and she coloured at the idea; but, recovering herself, said in a lively tone, "And pray, what is the usual price of an earl's younger son? Unless the elder brother is very sickly, I suppose you would not ask above fifty thousand pounds." (33.12-15)
Here, Colonel Fitzwilliam slips Lizzy a little hint that, while he thinks she's cute and all, he's not about to marry her. He may be the son of an earl, but he's the younger son, which means he's not going to inherit the estate—unless his older brother dies. Lizzy recovers by making a joke about how much it costs to marry an earl's younger son (i.e., how much money does the girl have to bring to the marriage?) but Fitzwilliam is serious: he has to marry a rich woman to support him in the manner to which he's become accustomed—his "habits of expense." He's our clue that, while this system of marriage isn't great for women, it's not great for men, either.
Quote 3
"In marrying your nephew, I should not consider myself as quitting that sphere. He is a gentleman; I am a gentleman's daughter; so far we are equal." (56.51)
You tell her, girl. Lady Catherine has just come to tell her exactly why she's not worthy to marry Darcy, and Lizzy sums up exactly why she is: "He is a gentleman; I am a gentleman's daughter." Sure, he has more money—but her birth and character are just as good as him. Yep, this is maybe Shmoop's favorite line in all of Pride and Prejudice.