I just received an interesting call from someone looking for a book that explains sacred music from a theological point of view -- one that gives a solid foundation and avoids polemics about the current troubles. That seems easy enough. But as I thought about it, nothing actually came to mind. He, on his own, then suggested Ratzinger's Sing to the Lord. I immediately agreed that this is the best book along those lines. But then neither of us could think of anything else. Everything else I can think of is historical, legislative, or pedagogical. Can anyone think of anything else?