Answer:
The theme is the baby
Step-by-step explanation:
The wedding gift, the baby, is one of the main themes of the story. Where the baby is presented to Jacque by his former lover who is dying. To which he accepts the child because it is his own, also it was part of the promise he made to it's dying mother. Then also to be presented, later, to Jacque's wife. To which she accepts the child and says "Well, we will bring up the little one.". It is quite unclear to me of whether or not the new born baby was representation of a wedding gift from Jacque's former lover to him, or from Jacque to his wife on their wedding night. Maybe it could simply of been a representation of Jacque's marriage to Berthe being the death of his love for the other woman. To die giving birth to a new love for the life he is going to have with Berthe. Where the new love is represented by the child, and Jacque presents to Berthe his complete and utter devotion to his love with her.