Music is an essential part of the Liturgy. It is easy to think of music as a kind of "adornment" that "enhances" the liturgy--like icing on a cake.
This is not quite the right way to look at it. Instead, think of music as like the eggs in the cake--the thing that binds it all together. Music is a part of our joyful identity as children of the Father. The old testament prophet Zephaniah describes the joy God has in us this way:
The Lord, your God, is in your midst, a mighty savior,
who will rejoice over you with gladness,
and renew you in his love,
who will sing joyfully becuase of you.
... the words of the psalmist prefigure the words and actions of Christ and provide an anticipatory model according to which we can form our character.
Beauty, then, is not mere decoration, but rather an essential element of the liturgical action, since it is an attribute of God himself and his revelation. These considerations should make us realize the care which is needed, if the liturgical action is to reflect its innate splendour.
Liturgical worship is given a more noble form when it is celebrated in song, with the ministers of each degree fulfilling their ministry and the people participating in it. [...] Gregorian chant, as proper to the Roman liturgy, should be given pride of place.
The Christian faithful who come together as one in expectation of the Lord’s coming are instructed by the Apostle Paul to sing together Psalms, hymns, and spiritual canticles (cf. Col 3:16). Singing is the sign of the heart’s joy (cf. Acts 2:46). Thus St. Augustine says rightly, “Singing is for one who loves, and there is also an ancient proverb: “Whoever sings well prays twice over.”