As with Jane Austen's other novel that has the same structure in the title (Sense and Sensibility), the themes of these seemingly-opposite states of being refer to more than one character conflict. In Pride and Prejudice, the central conflict is one directly connected to these two feelings as they are expressed by a number of characters. Elizabeth's pride is in conflict with Darcy's prejudice (or rather, his seeming judgmental air that he displays to her); but she also has to deal with the extreme pride of her family and in particular the pretentious social aspirations of her mother. But Austen redeems these conflicts, by showing that Darcy is in fact very tender towards Elizabeth and goes out of his way to protect her family's reputation, and help her save face when her sister's elopement is discovered.
It might also be a factor that truth and lies are of central importance in Pride and Prejudice:
Eliza'a prejudice was created initially by Darcy's off-hand manner towards her, but massively increased shortly after by Wickhams false account of his reationship with the Darcy family after the death of the father. This situation is the pivot of the whole story. Due to Bingley's initial attraction to Jane, he and Darcy were on their way to visit the Bennets when Wickham appered on the scene, possibly leaving a way open for Darcy and Eliza to remedy their original feelings towards each other. Jane Austen thus set the tone for a plot that might have turnd out very differently had Wickham's lies and deception not occured when they did. Wickham, indeed, is himself the main reason that Darcy suddenly became a total scoundrel in Eliza's eyes and created her unjust and unfounded prejudice against him.
Just a view.