Early in A Doll's House, the characters spend a good deal of time talking about their finances. Some are on the upswing, with the promise of free flowing cash in the future. Others are struggling to make ends meet. Either way, each character's financial status seems to a defining feature.
By deciding not to borrow money from Dr. Rank, Nora shows that she values their friendship and her own personal integrity.
Torvald's fear of debt is what drives Nora to commit forgery. In a way, it is the cause of all the problems in the play.