Written for One Audience

Johann Sebastian Bach was one of the most prolific composers in Western history — over a thousand works, from sweeping cantatas to simple keyboard exercises for his children. But tucked at the bottom of nearly every manuscript he completed, you'll find three letters: SDG. They stand for Soli Deo Gloria — Latin for "To God Alone be the Glory." Bach inscribed those letters even on routine teaching pieces, even on works he knew might never be performed publicly.…