Complex sentence: Grégoire's funeral was celebrated at the church of the Abbaye-aux-Bois; the clergy absented themselves in obedience to the archbishop's orders, but mass was sung by the abbé Grieu assisted by two clergy, the catafalque being decorated with the episcopal insignia.
Split into simpler sentences: Grégoire's funeral was held at the church of the Abbaye-aux-Bois. The clergy absented themselves in obedience to the archbishop's orders, but mass was sung by the Abbé Grieu assisted by two clerics, the catafalque being decorated with the episcopal insignia.