Possible Clues:

• Strange idea, chanted heavenwards in part of mass
• Section of mass that's somewhat dignified, sung as offered up
• Mass movement putting around Auden is good
• 'Latin mass prayer, Lamb of God (5,3)'
• Latin prayer
• Symbol of Christ in unusual guise and form
• Ideas revised about animal used in sacrificial offering
• Chant used in Holy Communion services
• Liturgical prayer
• The Latin for the prayer, Lamb of God