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.
~ St. Augustine, Confessions 9:6, 14
These wonderful words are quoted in the Catechism of the Catholic Church, which also reads as follows:
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 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." (Eph 5:19; St. Augustine, En. in Ps. 72,1: PL 36, 914; cf. Col 3:16)
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.
"Wonderful!" you'll say. Well, things are very different in real life... Here is what a former Lutheran pastor who is now Roman Catholic had to say a few years ago:
I am sorry to say Augustine’s wonderful words do not describe my experience with worship in the Church. Though at times I have been on the verge of tears, that was due to feelings of despair and not devotion. Far from drawing me into the Church, the manner in which the Mass is celebrated in most parishes constituted, in the end, the greatest stumbling block to my conversion.
The rest of the article is also worth reading.