While at times it may seem like music at Mass is simply background noise, the Church believes it should be much more than that.
In fact, the Church goes so far as to say that music is a greater "treasure" than the sacred images that surround us at Mass.
Music as a treasure
The Catechism of the Catholic Church is the place where we see the Church put a great emphasis on music in the liturgy:
The musical tradition of the universal Church is a treasure of inestimable value, greater even than that of any other art.
The Catechism is quoting Sacrosanctum Concilium, a document from the Second Vatican Council that focused on the liturgy.
One of the main reasons the Church puts a great emphasis on music is the fact that music is an integral part of worship:
"...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 solemn liturgy." The composition and singing of inspired psalms, often accompanied by musical instruments, were already closely linked to the liturgical celebrations of the Old Covenant. The Church continues and develops this tradition: "Address . . . one another in psalms and hymns and spiritual songs, singing and making melody to the Lord with all your heart." "He who sings prays twice."
Furthermore, music has the potential to speak a great amount of symbolism, lifting our souls to God by its words that match the liturgical actions:
Song and music fulfill their function as signs in a manner all the more significant when they are "more closely connected . . . with the liturgical action," according to three principal criteria: beauty expressive of prayer, the unanimous participation of the assembly at the designated moments, and the solemn character of the celebration. In this way they participate in the purpose of the liturgical words and actions: the glory of God and the sanctification of the faithful.
The Catechism then quotes from St. Augustine's Confessions as evidence to how music can move an individual to prayer:
How I wept, deeply moved by your hymns, songs, and the voices that echoed through your Church! What emotion I experienced in them! Those sounds flowed into my ears distilling the truth in my heart. A feeling of devotion surged within me, and tears streamed down my face -- tears that did me good.
When sacred music is done well and in harmony with the liturgy, it has a great capacity to lead our souls to God.