“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 a combination of sacred music and words, it forms a necessary or integral part of the solemn liturgy.” The Vatican Collection Vatican Council II Volume 1 Page 31 # 112.
In regards to the Liturgy of the Hours
" … in celebrating the liturgy, singing is not to be regarded as an extrinsic embellishment to prayer; rather, it wells up from the depths of a soul intent on prayer and the praise of God and reveals in a full and perfect way the community nature of Christian worship
The Liturgy of the Hours Volume 1 Page 93 # 270.
“The faithful fulfil their liturgical role by making that full, conscious and active participation which is demanded by the nature of the liturgy itself and which is, by reason of baptism, the right and duty of the Christian people. The participation (a) Should be above all internal, in the sense that by it the faithful join their mind to what they pronounce or hear, and cooperate with heavenly grace, (b) Must be, on the other hand, external also, that is, such as to show the internal participation by gestures and bodily attitudes, by the acclamations, responses and singing.”
“16. One cannot find anything more religious and more joyful in sacred celebrations than a whole congregation expressing its faith and devotion in song. Therefore the active participation of the whole people, which is shown in singing, is to be carefully promoted…”
The Vatican Collection Vatican Council II Volume 1 Page 84 # 15, # 16