What is an example of a symbolism in "A Doll's House"?

Arguably, one of the biggest symbols in the play A Doll's House is the season where the play is set. It is near the end of the year. Christmas and New Year's Eve are in the horizon. The weather is cold outside, yet, the Helmers keep warm inside with the proverbial fire on the hearth. 
Why is all of this symbolic?
It is symbolic because of the traditional and significant events that are celebrated toward the end of each year and especially during the Winter and Christmas seasons:
the birth of Jesus
the" birth"/start of a New Year
the end of the old and the welcoming of the new
If you think about it, there are several "rebirths" taking place in the play, in one way or another.
Mrs. Linde and Krogstad find one another, and they decide to restart their lives together.
Krogstad changes his ways.
Torvald discovers what Nora did and shows his true colors; he is no longer a loving husband but a judgmental and patronizing man.
Nora notices this and she, too, changes her ways. She decides to leave the family and go away forever. She realizes she has been a play thing, a doll. She is now reborn, and wants to be her own person. 

Nora [taking her bag]: Ah, Torvald, the most wonderful thing of all would have to happen.
Helmer: Tell me what that would be!
Nora: Both you and I would have to be so changed that— . . . our life together would be a real wedlock. Goodbye. [She goes out through the hall.]

All this being said, it is clear that New Year's Day will mark a totally different life for these characters. Nothing will be like it was before; the New Year will bring with it new lives, which could be happy or sad. Christmas, New Year's Eve, and New Year's Day (all celebrated during the Winter season) are definitely symbolic of a rebirth for the characters.