From the latest Pastoral Music as published by NPM:
"We all know the description of liturgical music's importance from the Constitution on the Sacred Liturgy Sacrosanctum Concilium (SC): 'The musical tradition of the universal Church is a treasure of inestimable value, greater even than that of any other art. The main reason for this pre-eminence is that, as sacred song united to the words, it forms a necessary or integral part of the solemn liturgy' (SC, 112). But how have we appropriated that description of 'sacred song united to the words . . . of the solemn liturgy'?
"Consider this example from the Chrism Mass: Diocesan liturgies often are unique, once-a-year (or even once-in-a-lifetime) events. They have particular needs and often require a specific repertoire. For example, the appointed text for the procession with the oils at the Chrism Mass is 'O Redeemer.' This text has no other liturgical use, but when done at the Chrism Mass its rich text helps reveal another layer of the mystery of the sacraments.
"Now while 'O Redeemer' may never be sung in a parish, this model of using specific (proper) texts from the Roman Missal or the Gradual can be of great benefit, for this processional hymn indeed weds the sacred song and the words of the liturgy. We have tended to get away from the 'propers' (texts assigned to specific days or liturgical actions), yet these can aid the people's participation.
"If you have gotten away from using proper texts, consider following the cathedral's example and add one or two a year. Chants for these texts can be found in a variety of sources (in both Latin and English), or they may be sung to another musical setting. The onees that seem easiest to find for congregation or choir (or a combination of the two) occur during Holy Week--Palm Sunday's 'Hosanna to the Son of David,' Holy Thursday's 'Mandatum novum' ('I give you a new commandment'), the Good Friday reproaches, or the sequence on Easter Sunday. You'll be surprised how much easier (and beloved) these become as you return to them year after year."