O QUANTA QUALIA is a chant tune from the Paris Antiphoner of 1681 and represents the "new" breed of French Roman Catholic diocesan tunes of the seventeenth and eighteenth centuries. The tune is often associated with Peter Abelard's twelfth-century hymn "O What Their Joy and Their Glory Must Be," which also has a new-heaven-and-earth focus. The tune name comes from the original Latin incipit of Abelard's text: "O quanta qualia…." Antiphonal singing may be desirable, as is singing in harmony, but the final stanza should be sung in unison and at a majestic pace as a finale/ doxology preferably with other instruments to enhance the festivity.

--Psalter Hymnal Handbook