The apple on the Twilight book cover holds significant symbolism, representing multiple aspects of the story and the relationship between Bella Swan and Edward Cullen.
Forbidden Fruit: The apple is often associated with the biblical story of Adam and Eve, where the fruit from the tree of knowledge of good and evil is commonly depicted as an apple. This connection symbolizes the forbidden nature of Bella and Edward's love, as it is dangerous and forbidden for a human to be romantically involved with a vampire.
Temptation: The apple is a symbol of temptation, and in the context of the book cover, it represents the temptation that Edward faces in his desire for Bella's blood. Edward struggles with his desire for Bella's blood, which is intoxicating to him as a vampire, paralleling the temptation faced by vampires in other vampire myths.
Feminine Symbolism: The apple is often associated with feminine symbols and themes, and its presence on the cover may represent Bella as the central female character in the story, around whom much of the plot revolves.
Iconic Scene: The cover also relates to a memorable scene in the book where Edward and Bella are sitting in a meadow, and Edward presents her with a hand-carved crystal apple as a physical representation of the meaning of the apple as a metaphor for their relationship.