The play is set during the holidays. Yes, it's Christmas time for the Helmers and New Year's is swiftly approaching. Chances are that this isn't random. Christmas and New Year's are both associated with rebirth and renewal. Several of the characters go through a kind of rebirth over the course of the play.
Both Nora and Torvald have a spiritual awakening, which could be seen as a rebirth. Nora's trials and tribulations wake her up to the pitiful state of her marriage. When the "wonderful thing" fails to happen, she realizes she'll never be a fully realized person until she severs herself from her husband. When she slams the door behind her, she is in a way reborn. Nora is not alone in her spiritual awakening, however. Torvald's last line, "The most wonderful thing of all?" (3.381), seems to indicate that Nora's words haven't fallen on deaf ears. Torvald, like his wife, has realized the complete inadequacy of his existence. By the end of the play, both Helmers have been reborn.
Krogstad and Christine are reborn as well. When these "two shipwrecked people […] join forces" (3.42), they each get a fresh start in life. Both of them view their renewed love affair as a chance for salvation. Krogstad hopes that it will help increase his standing with the community, and that Christine's influence will make him a better person. Christine is overjoyed that she will have someone to care for. She once again has purpose in her life. Yes, it seems that, in A Doll's House, 'tis the season for rebirth.