Effi Briest is an unusual novel for its time because it is from the perspective of a woman, causing it to be put in a similar literary category as Anna Karenina (by Leo Tolstoy). One major theme of this novel is the transition from childhood to adulthood, specifically for a woman in German aristocratic society in the mid-nineteenth century. This theme shows up in the clear differences between Effi and her husband, whom her family has pressured her to marry because of his wealth and status. Effi is young and highly imaginative and creative. She is interested in exploring the world with her senses, has vivid dreams, and believes that her house is haunted. Her husband, who is frequently gone on long business trips, is patronizing towards her, much older than she is, and interested in doing things to acquire social status rather than for the pure enjoyment of the experience. From the beginning, this stark difference between the two characters contrasts the joys of childhood with the dreariness and social rules of adulthood.

In portraying Effi's transition from childhood to adulthood, the novel also shows how women are punished by society for ignoring or choosing to defy social rules. Effi has an affair with a man who validates her sensual and adventurous nature, and she ends up having a child whose paternal line is unclear: it could be either her husband's or her lover's. Although the family moves away and the affair ends before her husband finds out about it, he does find out years later after finding letters between Effi and her lover. After this discovery, he divorces her. She is left with little money and loses custody of her daughter, who even years later does not want any relationship with her. Eventually, after a duel in which her former husband kills her former lover, Effi has a breakdown and must move in with her parents, and at the end of the book she is on her deathbed in their home.

Although this is a tragic ending to the story in many ways, it highlights the theme that women were constrained to very specific social roles. If they broke out of those social roles or prioritized their own pleasure, there was no longer any place for them in society or even in their families. While the book could be interpreted at Effi experiencing a justified punishment for her infidelity, at the end of the book her parents shoulder some of the blame for pressuring her to marry someone who didn't love her and whom she could never love. This indicates that it is possible that Fontane intended for the book to be a critique of the rigid social structure of German aristocracy, especially in the ways it policed the actions of women and not necessarily those of men.