During these chapters we discover about Elizabeth's change of heart about Wickham as she slowly discovers his true identity. This is suspenseful because we wonder what her reaction to Darcy will be now that she had openly insulted him, rejected his proposal, and on top of it took Wickham's side.
Additionally, Elizabeth pays a visit to Darcy's massive estate without knowing that he would be present. When she faces Darcy that second time, she notices further that he is a sweet man, that his servants love him, and that he has acted like a father to her sister.
Now is when the suspense comes: Darcy and Elizabeth are suddenly developing a relationship, and all seems bright until...blam! Lydia elopes with Wickham, bringing shame and distress to the entire Bennet family.
At this point, Darcy (who is a gentleman)felt that it would be a huge social challenge to be related to Elizabeth, as the sister of a 15 year old who eloped with a soldier already known for being a sleaze.
Therefore, the story reaches a climax with Darcy's renewed coldness against the Bennets and Elizabeth's breaking down in frustration against Lydia. Her fate and Jane's are sealed: They will be marked for life unless Lydia returns as a married woman.
Hence, once Lydia suspiciously marries without a problem, the graces come back to the Bennets, but it is here when Jane and Elizabeth find out that Darcy was directly responsible to pay for Lydia's dowry, to make Wickham man up and marry her, and to ensure the ceremony actually took place.
Here as readers we go from hating Darcy, to hating Wickham to loving Darcy to want to hang Lydia, and we breathe more comfortably knowing that Jane and Elizabeth will have a chance at love and that Lydia, although has gotten her dream wedding, we can foresee the quality of the relationship.