In addition to the first answer, Charlotte represents the typical plain country lady from Austen's time period. These women were raised with the goal of obtaining a husband who could not only provide security for his bride but who also--in many cases (such as the Bennet family's situation)--could provide support for the woman's family, especially if her family did not have an immediate male heir. While all aristocratic women such as Lady Catherine's daughter and Miss Bingley were also "required" to make suitable matches, their family's security and well-being didn't rely so heavily on their marriage match.
Charlotte specifically views finding and "securing" a suitable husband as a job because she believes it is her duty and that she is not quite good enough for anything else. She serves as a foil character to the independent, forward-thinking Lizzy.
During Jane Austen's time, marriage often amounted to no more than a business proposition. Few women at that time had the luxury of marrying for love because money and land were passed down through the male line, from father to son, leaving women without personal property or income. Therefore marriage to a man with money was the only way a woman could remain in her social class and be "secure." If a woman was not able to secure a husband, she could become a burden on her parents who are responsible for her care, or on other male relatives. Women were in a precarious position. Men also had a responsibility to marry someone of the same class. It was rarely an option to marry solely on the basis of love.
I love Jane Austen's Pride and Prejudice. What I think she means about this, is what the others have been saying, but also that your husband doesn't go around cheating on other women. You know? :)