I think it was priests and nobles because before the printing press was invented they made written copies of the bible.
Gospel. Gospel usually contains three part harmonies(divided by Alto, Soprano, and Tenor) and emphasizes triads.
One way to earn Glimmer quickly is to visit each planet and clean out all Region Chests. These are marked on the map as a cross with dot in the middle of it. Each one you open can give you some gear, but after reaching max Power level it's unlikely you'll find much value from that.
