An officer in the regiment stationed at Meryton, Officer Wickham possesses a charm that hides his dissolute, untrustworthy personality. He was godson to Darcy's father. However, Wickham betrayed Darcy by seducing Georgiana when she was only 15. He also spreads false rumors about Darcy throughout Hertfordshire and Meryton. Overall, Wickham is driven by self-interest, revealed by his many romantic engagements (or lack thereof, in the case of Elizabeth). He is also a static character and marries Lydia only because Darcy provides a financial incentive. In the epilogue, Austen implies that Wickham tires of Lydia after a certain point.
Bingley is open to the two youngest Bennet girls’ entreaties for a ball. The festivities serve to put the objective characters in close proximity with each other, moving all their relationships (for better or worse) forward; Lydia’s receptiveness to Wickham’s plan to run off without the benefit of marriage accelerates the objective story forward; Darcy willingly reevaluates Elizabeth’s family relations when he meets the Gardiners. He collaborates with them to return honor to the Bennet family which increases the pace toward the climax of the story; and so forth.
Hear hear. They were also ineffective; Lydia ends up in a marriage trap and poverty, and Mrs. Bennet throws away what agency she has with willful selfishness and silliness. If one has to insist on imposing modern values over these characters, the only one who stands up for herself is Charlotte, who walked deliberately and clear-eyed into exactly what she wanted. Lizzie was not embittered at her choice, but shocked, and disappointed in her friend, however she has to reevaluate her own prejudices when she sees how very well Charlotte has managed things, and how content Charlotte is.