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."
Catechism of the Catholic Church, 1157
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: “One who sings well prays twice."