Austen uses Elizabeth, Jane, Darcy, and Wickham to explore the related themes of Concealment and Approbation and Disapprobation.
concealment: the action of hiding something or preventing it from being known (Oxford Dictionary)
approbation: approval, praise; to commend (Oxford and Random House Dictionaries)
disapprobation: strong moral disapproval; condemnation (Oxford and Random House Dictionaries)
Jane is said by Charlotte to too thoroughly conceal her affection for Bingley from public scrutiny:
[R]eplied Charlotte, ... "[It] is sometimes a disadvantage to be so very guarded. If a woman conceals her affection with the same skill from the object of it, she may lose the opportunity of fixing him; and it will then be but poor consolation to believe the world equally in the dark. ... a women had better show more affection than she feels."
Elizabeth more than once playfully cautions Jane against concealing from her own scrutiny the faults in people she is acquainted with, which leads to concealment's twin fault of granting approbation for "the good of everybody's character":
[Elizabeth said,] "You never see a fault in anybody. ... I never heard you speak ill of a human being in your life. [...] But ... to take the good of everybody's character ...."
As predicted by Charlotte, Jane's character flaws of concealing special preference and granting approbation to all while viewing everybody's traits to be as beautiful as her own--as though she sees them shine through the light of her own beauty and goodness--leads her to lose Bingley. Darcy, seeing no "symptom" of love in Jane for Mr. Bingley and horrified at the empty, boastful pride of Mrs. Bennet, convinces Bingley that, though he feels love for Jane, she will never return his love with a love of her own and that the Bennets are beneath him. He advises Bingley to leave Netherfield and Jane. Later Darcy, to reinforce his planned separation of Jane and Bingley, practices concealment when he intentionally keeps from Bingley the news that Jane is in London at her Aunt and Uncle Gardner's home in Cheapside. Darcy later confesses to and apologizes for this concealment.
The Bingley sisters are co-conspirators of concealment with Darcy to separate Jane and Bingley because of their disapprobation for the Bennet family and of their earlier false approbation of Jane (they tolerate Elizabeth for her qualities though they feign no approbation for her). Jane falls from their good graces as a country acquaintance because, in their arrogant pride and prejudice, they have their own schemes for Bingley's happiness that do not include marriage to a woman--no matter how fine in character and beauty--who has embarrassing family connections and no wealth. As a result, they join in the effort to conceal from Bingley the fact of Jane's presence in London.
Wickham is perhaps Austen's crowning achievement in illustrating the twin themes of Concealment and Approbation and Disapprobation. What doesn't Wickham conceal? He conceals the truth about himself. He conceals his mounting debts. He conceals his truthful past history, giving a fairy tale version of half-truths. He conceals his conduct toward Miss Darcy, Darcy's sister Georgiana. He conceals that he is motivated by revenge (toward Darcy) and greed. He conceals his true sentiment of feeling for the heiress Miss King. He conceals his flight from Meryton and Brighton under cover of dark to escape debts. The harm Wickham's concealments cause drives the development of the plot and takes it to its climax and resolution.
Motivated by rightful family pride and deep feelings of approbation for Georgianna, Darcy participates in Wickham's concealments by concealing what he knows to be the truth about Wickham's true inner character. Had Darcy shuned concealment, no family would have welcomed Wickham at the hearths and no merchant would have extended him credit. Had Darcy not concealed the truth, Lydia's inner character may have remained intact and Mr. Bennet may not have been revealed as the bitterly neglectful parent that he was.
Through these characters, events and outcomes, Austen explores concealment, approbation and disapprobation and shows that falseness in applying any of these often results in terrible injustice and harm. This is the contrite lesson Darcy learns and makes amends for when he rescues Lydia from her own foolishness and provides for her marriage to Wickham and for Wickham's enlistment in another branch of the military, so as to provide them with an income. This is also the lesson that Elizabeth learns when she discovers that her prejudiced and hasty approbation of Wickham and disapprobation of Darcy have led to injustice and have helped to facilitate the harm Wickham wreaks in Meryton, Brighton, his regiment and in the Bennet family.