One of the most enlightening marriages to analyze in Pride and Prejudice is Charlotte Lucas's marriage to Mr. Collins. Charlotte's marriage is purely a marriage of convenience. While Elizabeth objects to the match at first, she later sees that it really is in Charlotte's best interest and that Charlotte is quite content. While Charlotte's father is a knight, he actually has very little fortune to distribute amongst his children. Hence, Charlotte knew that she would need to marry a man of fortune. Charlotte was also very plain and knew she would not likely receive another offer of marriage, therefore, she accepted Mr. Collins, as we see in the passage:
"It was the only honourable provision for well-educated young women of small fortune, and however uncertain of giving happiness, must be their pleasant preservative from want. This preservation she had now obtained; and at the age of twenty-seven, without having ever been handsome, she felt the good luck of it." (Ch. 22, Vol. 1)
Even though at first Elizabeth thought that Charlotte was making a huge mistake, when she goes to visit Charlotte at Huntsford after the marriage, she sees that she was mistaken. Elizabeth sees that Charlotte is comfortable in her new home and that Charlotte even enjoys it (Ch. 5, Vol. 2). Elizabeth soon agrees that Charlotte "seems perfectly happy" and that "it is certainly a very good match for her" (Ch. 9, Vol. 2). Austen uses Charlotte's comfort and happiness in her marriage, despite the fact that Mr. Collins is a ridiculous man, to show that sometimes a practical, sensible, marriage of convenience actually is the best thing. As Charlotte herself states, "Happiness in marriage is entirely a matter of chance," even if you are in love with the person (Ch. 6, Vol. 1). Therefore, Austen is pointing out that sometimes it is wisest to marry with your head for practical reasons, than to marry with your heart for love.
Austen's philosophy on marrying wisely relates to the overall theme of prejudice. Elizabeth was prejudiced in thinking that marrying for love is the only practical marriage and that Charlotte could not possibly be happy with Mr. Collins. Elizabeth's blind prejudice soon dissipates when she sees Charlotte comfortable and happy.