During the 19th century in which Pride and Prejudice is set, most marriages were unlikely to be happy and were mostly for the sake of financial gain or necessity. While Mr. and Mrs. Bennet do have a characteristically unhappy marriage, it is really Charlotte Lucas's marriage to Mr. Collins that best portrays the social circumstances of the time surrounding marriage.
Mr. and Mrs. Bennet's marriage was a bit unusual in that Mr. Bennet actually married beneath his class, although it was becoming more common place for the genteel class to marry the working class. Mrs. Bennet comes from the working class and has two siblings that are still in that class, although they are quite successful. It is Elizabeth's opinion that it is partially due to her mother's lower-class upbringing that she has very little understanding of either principles or decorum and is raising her youngest daughters to be vain, selfish, ridiculous flirts. In addition, Mrs. Bennet's lack of principles causes strife in the marriage. As Austen phrases it, Mr. Bennet married her simply because she was young and beautiful, and then later realized he "had married a woman whose weak understanding and illiberal mind had, very early in their marriage, put an end to all real affection for her" (Ch. 42). By "weak understanding," Austen is referring to Mrs. Bennet's lack of understanding principles, and by "illiberal mind," Austen is referring to her as selfish, showing us just how dissatisfied Mr. Bennet was with his wife's character. While the Bennet's unhappiness in marriage may have been characteristic, it was not characteristic for the gentry to marry the working class, although it was becoming more common. Therefore, despite their characteristic unhappiness, the Bennets do not represent the most typical type of marriage in this period.
Instead, it was far more common for couples to marry based on either financial gain or need, just like Charlotte Lucas needed to marry Mr. Collins out of financial necessity. While Charlotte's father was newly knighted due to his service as mayor of Meryton, Austen points out that Sir Lucas quit his trade business and bought an estate to live the life of a gentleman far too soon. Instead, he should have kept working the business and left it to the next generation to purchase an estate. The result is that Sir Lucas has very little fortune for his children to inherit, and Charlotte absolutely must marry to insure that she is well provided for as she gets older. Even though Mr. Collins is a ridiculous man, he is a good choice because he will be inheriting the Bennet's Longbourn estate. Despite the fact that Mr. Collins is very vain and behaves in absurd ways, Charlotte actually states that she is very content in the marriage. Charlotte has received from the marriage exactly what she wanted, "a comfortable home" (Ch. 22). As Elizabeth observes, "When Mr. Collins could be forgotten, there was really a great air of comfort throughout [the home]" (Ch. 28). While it wasn't impossible for a marriage based on financial need to be a content marriage, it may not have been very common. Therefore, while Charlotte's marriage is more representative based on motive for marriage, her emotional status in marriage may not have been very characteristic. Instead, the Bennet's unhappiness may have been more characteristic, even though it was more of an unusual marriage.