Symbolism, Imagery, Allegory
"Hey, what's up with the apple?" you may be wondering, especially if you've read the copy of Twilight that has the original cover. That question ran through our heads, too. We thought we were going to be reading a love story with vampires, not an ode to shiny fruit. Then we saw the epigraph. Aha!
We highly recommend that you check out "What's Up with the Epigraph? to get the full story, but the quick answer is that the apple is a symbol for temptation. The Biblical Adam and Eve were banished from the Garden of Eden for giving into temptation and eating fruit from a forbidden tree. (You can read more on Adam in Eve in Genesis 3). Traditionally in art and literature, the fruit that Adam and Eve eat is an apple.
Aside from the apple on the original book cover, the apple pops up in the Forks High cafeteria in Chapter 10. Bella sits there rolling around that apple in her hands, as though she's trying to decide whether to eat it or not. Keep in mind that this happens to coincide with the period of time when Bella is trying to figure out exactly what she should do about the Edward situation. She's not quite sure if she should cave to temptation and pursue a relationship with Edward despite the danger.