Complex sentence: The title refers to the laymen who were employed to sing musical sections of church services during the Middle Ages; at the time, this was often music which was evolving into a format too complicated to be sung by many ordinary clerks and priests.
Split into simpler sentences: The title refers to the laymen who were employed to sing musical sections of church services during the Middle Ages. At the time, this was often music which was evolving into a format too complicated to be sung by many ordinary clerks and priests.