Compare and contrast between the two kinds of marriage in "Pride and Prejudice"

Members of the social class of the Bennet sisters, and particularly in Jane Austen's time, women married for financial security, to have a home of their own, to secure their future beyond their father's home. In the case of the Bennet sisters, they will have no home once their father dies, they have no brothers, so the home will pass to the next male heir in the family, Mr. Collins.  That is why Lizzie's rejection of Mr. Collins is so profound, she will not sacrifice herself to protect the family home.

The two types of marriage that are depicted in Pride and Prejudice are marriages made for long-term security, and marraiges made for love.   An example of a marriage of security is that of Charlotte Lucas and Mr. Collins.  A marriage made between a woman with no prospects who accepts a proposal because she needs financial security and a home of her own. 

Charlotte does not marry Mr. Collins because she loves him, it appears to be just the opposite, she does not love him, but she does respect him.

Both the Bennet sisters want to marry for love, and they both do in the end.  However, they are also given the added bonus of becoming financially wealthy as well.

Jane Bennet, at first, appears to be making a good match with Mr. Bingley for both love and financial security.  This works out in the end, but for a time it appears that Jane will not be so lucky as to be able to marry for love, with the bonus factor being that she will also be very rich.

Lizzie Bennet does not want to marry for security, she wants to marry for love.  Both Lizzie and Jane are lucky in Pride and Prejudice to be able to marry for both love and money. Jane Austen was in love with a young man and ultimately had to give him up because he was not permitted to marry her because of her social class.  The young man ended up marrying a girl who was wealthy and Jane Austen remained unmarried.  But she had brothers who protected her and her sister while they lived in the family home looking after their mother.

Lydia's marriage falls into another category.  She is a silly girl who makes spontaneous decisions without thinking.  She ends up married to Wickham because of Darcy, it is a necessity that they be married in order to save the Bennet family reputation.