The liturgical text must be sung as it is in the books, without alteration or inversion of the words, without undue repetition, without breaking syllables, and always in a manner intelligible to the faithful who listen."
The guidance quoted is not absolute in the way it is expressed. I don't find Vivaldi's paean of praise undue in it's repetition, or unintelligible. But there is music in use in which the separate voices have meaning obscured by repetitions. Perhaps not in liturgical use, Handel comes to mind (But I should check before making rash statements).without undue repetition, ... in a manner intelligible to the faithful
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