HELMER: "Suppose, now, that I borrowed fifty pounds today, and you spent it all in the Christmas week, and then on New Year's Eve a slate fell on my head and killed me." (1.16)
Torvald is ever the pragmatist when it comes to financial matters.
HELMER: "Bought, did you say? All these things? Has my little spendthrift been wasting money again?" (1.11)
Nora is constantly accused of wasting money when, in reality, she keeps barely anything for herself, all in an effort to pay back the loan that saved her husband's life.
HELMER: "There can be no freedom or beauty about a home life that depends on borrowing and debt." (1.21)
Torvald's absolute horror of debt is what forced Nora to deceive him in regards to the loan that saved his life.
NORA: "You might give me money, Torvald. Then I will wrap it up in beautiful gilt paper and hang it on the Christmas Tree." (1.38-1.40)
There's a good chance that Nora wants money for Christmas just to pay down her secret debt.
NORA: "Christine! It will be splendid to have heaps of money and not need to have any anxiety, won't it?" MRS. LINDE: "Yes, anyhow I think it would be delightful to have what one needs." (1.114-1.115)
Nora seems to show very little sensitivity to her friend's financial problems.
KROGSTAD: "Or perhaps that you have some expedient for raising the money soon? NORA: "No expedient that I mean to make use of." (2.259-2.260)
Nora is referring to her decision not to borrow money from the lovesick Dr. Rank. Why doesn't she want to borrow it from him? Does she not want to manipulate him? Or does she feel like she'd be selling herself in some way?
KROGSTAD: "How will you be able to prevent it? Am I to understand that you can pay the balance that is owing?" (2.257)
Nora's debt gives Krogstad power.
KROGSTAD: "I shall only preserve it—keep it in my possession. No one who is not concerned in the matter shall have the slightest hint of it." (2.263)
Rather than blackmailing the Helmers for money, Krogstad is seeking to regain his reputation... showing what he truly values as a character.
HELMER: "I hear [Krogstad] is a good worker, too. But I knew him when we were boys. […] this tactless fellow lays no restraint on himself when other people are present. On the contrary, he thinks it gives him the right to adopt a familiar tone with me." (2.117)
Looks like Torvald has been hiding something as well. This is the first time he mentions that he used to know Krogstad.
Mrs. Christine Linde
MRS. LINDE: "You must not forget that I had a helpless mother and two little brothers. We couldn't wait for you, Nils; your prospects seemed hopeless then." (3.22)
Christine's need of money for her family forced her to sacrifice her love for Krogstad.