The central theme of Pride and Prejudice has to do with the Bennett family having five daughters. The members of the family are of the class of "gentry", meaning that it would be a violation of class norms for them to actually work in order to earn money; instead, they live on inherited wealth. There are two ensuing economic problems.
First, Mr. Bennett having no living son, his estate devolves on Mr. Collins, leaving nothing capable of supporting his daughters after he dies (although he is in healthy middle age in the novel, obviously his daughters will be likely to survive him). Since his daughters have no means of being self-supporting, they must make good marriages to continue to live as gentlewomen.
Unfortunately, the dowries of the daughters are small and the number of eligible bachelors of the right class limited. Thus the marriage issue in the novel is not purely a romantic one but fundamentally an economic one.