Passion vs. Responsibility
When Effi moves to Kessin with her new husband, she imagines all sorts of wonderful versions of her life. Reality bites, however, when she quickly learns that her fate was that of the trophy wife. She is neither cherished nor empowered. She yearned for this marriage so badly before, though, because she desired a powerful man who could provide for her and give her a strong social reputation, in accordance with the expectation which her parents placed upon her. Growing up, her only objective was to marry an aristocrat, as her parents had taught her. In adulthood Effi quickly becomes tempted by the passion of Major Crampas. He's made his reputation as a ladies' man, understanding every woman's desire for passion and indiscretion. He tempts her with an affair of emotion and intrigue.
Isolation
Geert's response to Effi's affair is a prompt divorce. He wants to separate his reputation from hers as quickly as possible. He probably also wants to punish her with the rejection, but she was already alone in the marriage. Following suit, her parents also disown Effi for the affair. They don't want to tarnish their family reputation with her indiscretions, having only encouraged the marriage for social advantage in the first place. Next comes the real insult. Geert raises their daughter, Annie, to hate her mother, filling her head with vile thoughts. He ensures that Annie will never trust her mother, which she doesn't. According to these three responses, one can see that the society functions through shame. If an individual departs from socially acceptable actions, they are punished with isolation -- shunned much like the outcasts of Puritan society. Effi's various relations hope to punish her unacceptable behavior with complete social isolation, making her a pariah.
Social Commentary
Fontane clearly writes this novel as a social commentary. His heroine follows the role of Anna Karenina and Madame Bovary, the disgraced wife. Effi's plight is not altogether different from most housewives of the day. According to tradition, these women of the aristocracy and upper class were supposed to quietly rest upon their husband's titles and not to demand anything of him. They weren't allowed to seek out adventure or romance or accomplishment; those were shameful to the family. When Effi discovers firsthand the full sacrifice of these expectations, she revolts. She cannot bring herself to wait quietly at home, having no promise of ever finding something worth doing or someone worth meeting. Because her story is a tragedy, Fontane uses her death to condemn German society of the time for placing such impossible standards on women. After all, Effi is a product of her environment and receives no help from the people around her.