Austen lived during a period that did not provide much opportunity for social mobility, particularly for women. Marriage and social mobility were intricately linked. Perhaps the clearest example of Austen presenting this theme in Mansfield Park is in the extremely disparate situations of Fanny’s mother and two aunts.
Of these three, one sister—Fanny’s mother—marries a poor man and is consigned to living at the bottom of the social rung. Another marries a wealthy baronet, enjoys incredible economic success, and moves upward socially. Austen ascribes this ascent to her beauty and luck; it is clear that marriage was her only route to achieve social mobility. The third sister marries a man with a respectable profession, a reverend, and schemes to improve her social situation by making herself indispensable to the sister who has achieved marital and social success. Austen writes,
Miss Maria Ward, of Huntingdon, with only seven thousand pounds, had the good luck to captivate Sir Thomas Bertram, of Mansfield Park … and to be thereby raised to the rank of a baronet’s lady, with all the comforts and consequences of an handsome house and large income. … She had two sisters to be benefited by her elevation. … Miss Ward, at the end of half a dozen years, found herself obliged to be attached to the Rev. Mr. Norris, a friend of her brother-in-law, with scarcely any private fortune, and Miss Frances fared yet worse.
Fanny’s mother married for love and lives a life of poverty. Weighed down by her inadequate means to support her family, she essentially gives Fanny over to her wealthier sister in order to lighten her own family’s financial responsibility and have one less mouth to feed. She cannot supply Fanny or her other children with the education or material possessions that Fanny’s cousins enjoy, and Fanny witnesses their disparate situations firsthand when she moves to Mansfield Park.
The link between marriage and social mobility for women is also seen in the stories of the cousins, Fanny and Maria Bertram. Although Fanny enjoys the benefits of the family's greater knowledge of books and culture and is able to receive an education that is far superior to anything she could have achieved at home, she retains her inferior social status as a poor relation living at Mansfield Park.
However, eventually, her uncle decides that she is eligible to be presented to society. This is not an affirmative acknowledgement that she has achieved social parity with his daughters, but it does represent her opportunity for upward social mobility expressed purely through marriage as the vehicle for that mobility. If she marries well, specifically if she marries Henry Crawford, she can achieve parity with her cousins. Conversely, Maria achieves downward social mobility when she leaves her husband for a clandestine affair with Henry Crawford, which ruins her reputation and consigns her to a lifestyle well below that to which she originally aspired.