Symbolism, Imagery, Allegory
Book 'Em
Everything is Illuminated is a book about writing, so it's fitting that it's a book filled with fictional books.
One of these is The Book of Antecedents, which is a really just a book of events that the villagers keep to say, essentially, "we exist"! The people are writing for the sake of writing: "When there was nothing to report, the full-time committee would report its reporting, just to keep the book moving, expanding, becoming more like life: We are writing… We are writing… We are writing…" (24.11). In other words, it's basically the 19th-century equivalent of wearing a webcam everywhere you go. (Yes, even back then, people were obsessed with tracking every single mundane detail of life.)
Another book within a book (within a book, since part of Everything is Illuminated is the book that Jonathan Safran Foer the character is writing…) is The Book of Recurrent Dreams. Like the Book of Antecedents, this book is a way for villagers to record everything that didn't happen… but could.
In fact, one of the dreams seems to come true: Brod's dream of the raid on Trachimbrod, which she calls "The dream of the end of the world" (33.22). Given that we have no idea where Brod came from, or, if she was even human in the first place, we have to wonder if she was just a dreamer or actually a prophet.