The forest isolation
A forest isolation is a common literary motif, often associated with women, but in this story, it isn't a witch in her forest hut, living alone and sipping potions, but rather, it's a lonely kept housewife, sipping the potions of her husband, which are wine and cigarettes. In other words she doesn't have a good source of nutrition or support, either metaphorically or otherwise. She is completely alone, representing her husband's inhumane treatment of her. It's like he doesn't even notice she is a real person.
Bernard's defense in court
The fact that Bernard defends Theresa is the best symbolic signal in the book to show the reader the caliber of his dysfunction. It is not enough to him that she has literally tried to poison him. He still would rather continue in his "relationship" with her than to see her tried for her crimes against him. This is a symbolic demonstration of his manipulative nature and the creepy way he dominates his wife by going out of his way to be in control.
The archetypal slave wife
His wife ends up being Bernard's slave. She does what he wants, and when he wants her around, she is, and when he wants her to leave him alone, then she does, until he needs something. She represents a kept housewife in the grips of marriage, tied by commitment to someone who makes the most of her service, taking advantage of her, keeping her away from her friends and family.
The savior sister
It isn't just anyone's sister who saves Theresa from Bernard—it's Bernard's sister. Because she is a savior to Theresa, the reader might liken her to a deus ex machina, as if she were a messiah figure, which means that ironically, it is a familial woman who saves Bernard's wife from him. She represents the love between women and the support network among healthy communities which helps to prevent chronic abuse against women.
The weak tyrant
The husband is a weak tyrant. His archetypal behavior comes from his nightmarish experience of powerlessness. Having weakened himself morally by indulging in his appetites, which is clearly evident from his chronic sloth and alcoholism, Bernard has become dependent on his wife emotionally. He feels he needs her, but that makes him despise her, and the relationship he has with her is one of manipulation and domination.
