It used to be there was only a smattering of titles each season on the effects of faith on politics, but all of that has changed since 9/11. Now the lists are crowded with books on the hardening of lines between left and right, and the ways religious beliefs figure into positions on a variety of issues. And as publishers woo younger readers, trying to turn them into the next generation of book buyers, titles that deal with religious themes in movies, TV, on the Web and in popular music have also been more evident. For many Americans, religious commitment—or the lack of it—shapes behavior in the voting booth, the music store, the movie theater and, perhaps especially, the bookstore.