Complex sentence: They brought the result of their labours to the Chapter of Paris (1246), which approved the compilation and ordered its exclusive use by the whole Order and approved the "Lectionary" which had been entrusted to Humbert of Romains for revision.
Split into simpler sentences: They brought the result of their labours to the Chapter of Paris (1246), which approved the compilation and ordered its exclusive use by the whole Order. This same chapter approved the "Lectionary" which had been entrusted to Humbert of Romains for revision.