The basic difference between music in church in the Middle Ages and now is that now the music is usually a matter of free choice by the minister — think of gospel music — whereas then it was fixed by a higher authority. This was true even in humble parish churches — that is, local churches for ordinary people — and all the more so for the higher ranks of Christendom: monks and nuns in monasteries, and priests and clerics attached to the great cathedrals.

The higher authority was called the liturgy. A whole set of services was arranged according to the calendar, specifying how to worship in summer or winter, on Sunday or a weekday, at night or in the morning, and how to celebrate All Saints’ Day or Christmas, mark the beginning of Lent, or pray to the Virgin Mary or a patron saint.

All the largest world religions — Islam, Hinduism, and Buddhism as well as Christianity and Judaism — have complex systems of worship, or liturgies, and they all involve singing or chanting. Zen, for example, has a particular liturgy within Buddhism. Liturgies also include prescriptions for dress, incense, candles, movements, and so on. In Christianity, the central dates of the liturgy concern the life of Christ (his birth at Christmas, his crucifixion and resurrection at Easter) and the main saints, especially the Virgin Mary (her birthday, the day she ascended to heaven).

Monks and nuns in the Middle Ages spent an amazing amount of their time in prayer. Besides the Mass, a lengthy ceremony that might happen more than once a day, there were no fewer than eight other prayer services through the day and night. Large portions of all these services were sung. Each prayer was assigned its own music, in traditions built up over the years through small additions and adjustments to a traditional prototype.

Listening to this singing was not so much listening as worshipping, while allowing music to expand the devotional experience. Hearing liturgical chant today, one feels less like a listener in the modern sense than like a privileged eavesdropper, someone who has been allowed to attend a select occasion that is partly musical, but mainly spiritual. The experience is an intimate and tranquil one — cool and, to some listeners, especially satisfying.