How does the relationship between Krogstad and Mrs. Linde serve to emphasiz certain qualities in the Helmers’ marriage?

I think that a major theme behind the relationship between Krogstad and Mrs. Linde is forgiveness. Mrs. Linde sacrificed her love to marry Torvald for financial reasons. This might sound superficial on the surface of things but she really did it to support her mother and brithers. Mrs. Linde felt she had no alternative. Still, both Mrs. Linde and Krogstad maintained a friendship with intimacy and forgiveness.