In Act 2, Why did Ibsen decide to insert Dr.Rank's confession of Love for Nora in the action of the play?

At first, Nora’s interaction with Dr. Rank is similarly manipulative. When she flirts with him by showing her stockings, it seems that she hopes to entice Dr. Rank and then persuade him to speak to Torvald about keeping Krogstad on at the bank. Yet after Dr. Rank confesses that he loves her, Nora suddenly shuts down and refuses to ask her favor. She has developed some moral integrity. Despite her desperate need, she realizes that she would be taking advantage of Dr. Rank by capitalizing on his earnest love for her.