Austen uses pairings and doubling in some of her novels to show that human relationships are based upon acceptance of others' faults and awareness of ones' own foibles. These pairings are often personal qualities or behaviors that seem at odds with one another; in 'Sense and Sensibility' for example, the sisters have very different approaches to matters of love; the one who lives through 'sense' feels too strongly and gives her heart too trustingly, while the one who lives by 'sensibility' doesn't expose or share her feelings. Both sisters find that this approach causes hurt feelings. In 'Pride and Prejudice' these opposite qualities can both be found in both Elizabeth and Darcy, the two main characters, but also in the people who most affect their ability to be together: their parents, Elizabeth's sisters, and the various suitors who come and go in the Bennett household.
The final message that Pride and Prejudice gives us is that love conquers all. A message that Jane Austen was determined to write into her novels since she observed that it was impossible to achieve in real life. If you know something about Jane Austen's life and personal experience with love, as well as that of her sister, Cassandra, you easily see why she wrote such happy endings for Lizzie and Jane Bennet.
In Austen's world, 18th century society did not look as kindly on the marriages that Jane and Lizzie are so fortunate to make. In fact, Lizzie Bennet marrying Mr. Darcy would be unheard of in Austen's social circles. Austen wrote about the wonderful marriages that the Bennet sisters made to run contrary to her own experience and that of her own sister Cassandra.
Significant in her work is the importance of love in marriage, that is the true message that she leaves the reader with at the end of Pride and Prejudice. Jane Austen's view that love was the most important factor in marriage is made very obvious when Lizzie rejects Mr. Darcy's first proposal.
Consider, the position that her family is in, five daughters, the family home willed to the next male heir, Mr. Collins, yet Lizzie feels no urgency to accept Mr. Darcy's proposal of marriage, even though he is astoundingly rich and handsome. She won't consider him because, at the time, she did not realize that she loved him.