Death, in the end, hovers over Frank Schaeffer's "Voices From the Front: Letters Home From America's Military Family." This is not a depressing book. Not at all. The letters are almost invariably uplifting, full of simple nobility and a certain kind of life-sustaining joy. But "Voices" is a book about war, and that inevitably means death -- killing the enemy, watching your countrymen being killed and contemplating the ever-present possibility of your own death. Love letters, camp-life updates, care-package requests, notes of appreciation or longing -- the business of killing or being killed adds meaning to every communication in the...