Calvin on Music and Prayer

And surely, if the singing be tempered to that gravity which is fitting in the sight of God and the angels, it both lends dignity and grace to sacred actions and has the greatest value in kindling our hearts to a true zeal and eagerness to pray. Yet we should be very careful that our ears be not more attentive to the melody than our minds to the spiritual meaning of the words. Augustine also admits in another place that he was so disturbed by this danger that he sometimes wished to see established the custom observed by Athanasius, who ordered the reader to use so little inflection of the voice that he would sound more like a speaker than a singer. But when he recalled how much benefit singing had brought him, he inclined to the other side. Therefore, when this moderation is maintained, it is without any doubt a most holy and salutary practice. On the other hand, such songs as have been composed only for sweetness and delight of the ear are unbecoming to the majesty of the church and cannot but displease God in the highest degree.

…Lastly, we should hold that the tongue is not even necessary for private prayer, except in so far as either the inner feeling has insufficient power to arouse itself or as it is so vehemently aroused that it carries with it the action of the tongue. For even though the best prayers are sometimes unspoken, it often happens in practice that, when feelings of mind are aroused, unostentatiously the tongue breaks forth into speech, and the other members into gesture.

John Calvin
Institutes of the Christian Religion

Recommended:

Vincent Cheung, Prayer and Revelation

Gordon Clark, Sanctification

John Owen, Communion with God