The Catechism in Questions & Answers

678. What is the function of music in the divine service?

The purpose of music in the divine service is to bring praise and glory to God (cf. Psalm 150). It therefore has a serving function.
It can deeply move the soul, prepare the congregation for the proclamation of the word, and underscore the word of God. Singing—be it by the congregation or the choir—and instrumental music expresses and imparts courage, strength, and confidence. In times of sadness and hardship, music can provide comfort.
Music and silent worship before the divine service help those attending the divine service gather their thoughts, and prepare the way for the proclamation of the word. In the singing of the congregation, all present are actively involved in the divine service experience. Before the celebration of Holy Communion, the congregation can attest to their feelings of repentance in a hymn. In the hymn sung during the celebration of Holy Communion, they express their love and gratitude toward God.