Of course it's the power of the usually canonic forms and the occasional passing tone discords into glorious harmonic resolutions that invite a wider range of interest than among just the community of literal believers, many of whom seem to prefer insipid Modern Christian Music. I had the pleasure of watching a sight reading choral singer join a shape note sing this afternoon more or less by accident and just about levitate over Northfield and All Is Well, among others. She'd never heard any of it before. It was great to watch! (Great to hear too, as she was a good soprano.)