a capella chorales

What is it about singing good, strong Lutheran chorales, in 3- or 4-part harmony, without accompaniment? It's lush and rich. Our choir director (aka, pastor) doesn't like music to drag. And yet, when we sing in parts during the opening for Bible class or during chapel (that is, when there is no organ), the music slows down, almost like we're caressing the chords, enjoying the richness, letting it all soak into rafters and seep into our ears and our hearts.