Mr. Collins to be sure was neither sensible nor agreeable; his society was irksome, and his attachment to her must be imaginary. But still, he would be her husband. — Without thinking highly either of men or of matrimony, marriage had always been her object; it was the only honourable provision for well-educated young women of small fortune, and however uncertain of giving happiness, must be their pleasantest preservative from want. This preservative she had now obtained; and at the age of twenty-seven, without having ever been handsome, she felt all the good luck of it.
page 83-84, Volume I, Chapter XXII of Pride and Prejudice
Austen, Jane, and Donald J. Gray. Pride and prejudice: an authoritative text, backgrounds, reviews and essays in criticism. 3rd ed. New York: W.W. Norton, 2001. Print.
In this passage, Charlotte has accepted the extremely expedient proposal given by the unbearable Mr.Collins. She has done this merely for the stability that would be granted by such an engagement. She required such a match to prevent her from becoming an old maid without a home or a fortune. As a realist of the time and the society that she lived in, she was forced to marry for money and social as well as financial security, as opposed to marrying for love.