No outsiders are ever admitted to the monastery of Saint-Gilbert-Entre-les-Loups, hidden deep in the wilderness of Quebec, where two dozen cloistered monks live in peace and prayer. They grow vegetables, they tend chickens, they make chocolate. And they sing. Ironically, for a community that has taken a vow of silence, the monks have become world famous for their glorious voices, raised in ancient chants whose effect on both singer and listener is...