As the title suggests, the main themes in Pride and Prejudice really are pride and prejudice. Elizabeth is shown to be guilty of prejudicially judging Darcy to be prideful. In addition, it turns out that improper pride is actually the reason behind Elizabeth's prejudice. Finally, while Darcy is recognized as feeling above his company, the reality is that he really is the most noble character in the book and found to actually not have any improper pride. We know that pride and prejudice are the most dominant themes in the book because it is these two themes that create the main conflict in the story, which is Elizabeth's dislike of Darcy and Darcy's unrequited love for Elizabeth, also expressed as character vs. character.
Elizabeth first realizes the error of her judgements after reading Darcy's letter explaining his thoughts on her family's behavior and his history with Wickham. It is after this that she realizes she foolishly judged Wickham to be the most amiable man she's met simply because he is conversational and friendly. Likewise, she realizes that she judged Darcy to be a despicable man partially because he is reserved and standoffish and partially because of what Whickham told her about Darcy's treatment of him, which turned out to be all lies. As Elizabeth herself expresses it:
How despicably have I acted ... I, who have prided myself on my discernment ... Had I been in love, I could not have been more wretchedly blind. (Ch. 36)
Hence we see that it is truly Elizabeth who has had the wrongful pride and that her pride has caused her to prejudicially misjudge both Darcy and Wickham.
Darcy expresses a very central point towards the beginning of the book. He argues that "pride--where there is a real superiority of mind, pride will be always under good regulation" (Ch. 11). His point is that people who genuinely do have a greater, more intelligent understanding than others and who act upon principles and morals while others fail to do so really should feel genuine pride. And he is shown to be right. All throughout the novel Austen shows us that there really are people who have limited sense and understanding, such as Mrs. Bennet, and who act in immoral, imprudent ways, such as the rest of the entire Bennet household, especially Lydia, and Wickham. Darcy, on the other hand, always acts upon morals and principles and even rescues Lydia and the whole Bennet household from disgrace. Hence, Darcy really is shown to be superior in both sense and morals to other characters in the book, which is why Elizabeth says towards the end of the novel, "Indeed he has no improper pride" (Ch. 59). However, Darcy is also proven to have felt himself to be above his company and to have looked down on others simply because of their connection with the merchant class. Darcy makes this realization by the end of the novel and repents having acted upon his principles with "pride and conceit" (Ch. 58). Hence we see that Darcy had genuine reason to appreciate, or take pride in, his sense and morals, but was also guilty of acting in a way that judged and criticized others.
The main theme which is mentioned in Pride and Prejudice is love. In this book it contains a love story between Darcy and Elizabeth. In this classic, there two main problems between them. First of all Elizabeth's pride causes her to misjudge Darcy and is given a wrong first-impression. While this problem also is created another one is created due to Darcy's prejudice against Elizabeth's low social class, which causes him to be blinded from Elizabeth's many virtues, for a time.