The first appearance of instrumental music in church worship was about the sixth century A.D. The exact date of its introduction varied in different localities; but it can safely be concluded that there was no general practicing of it until after the eighth century, and even after this date it was long resisted by leading religionists.
The information to follow presents historical background about the practice of the primitive church regarding music. The scholars who are quoted all concur that instrumental music was not part of the worship of the primitive church.
Syrian monasteries and churches were scenes of early musical elements in worship as well. Antiphonal psalmody and hymns were first present in Syria and then spread to Milan and further west. Antiphonal psalmody was also evident in the Jewish temples. Antiphonal singing means that two choruses sing "back and forth" to each other, much as an echo, though not always identical music.
At the time of the Reformation - in the 16th Century - the reformers wanted the liturgy to be said in the vernacular. They also insisted upon hymns which could be understood and sung by the people, and they wished to get away from plainchant hymnody, most of which could only be performed by monks.
There were instruments of music of many and various kinds that were in use during the age of the apostles. Their never being introduced into the worship service by the apostles or the early Christians is conclusive evidence that they were undesirable as a means of expressing praise. Instrumental music is incompatible with the direction for singing given in the New Testament.
During the middle ages, the newly emerging Christian Church came to dominate Europe, administering justice, instigating "Holy" Crusades against the East, establishing Universities, and generally dictating the destiny of music, art, and literature. It was during this time that Pope Gregory I is generally believed to have collected and codified the music known as Gregorian Chant, which was the approved music of the Church. Much later, the University at Notre Dame in Paris saw the creation of a new kind of music called organum.
From the references of the Bible, the Hebrews sang and used various musical instruments in their worship. Associated with religious sacrifice were the shofur, or ram's horn trumpet, and the hazazna, another trumpet. On secular occasions, the Hebrews played the lyre, and a type of flute called the ugab.
It was the great Isaac Watts (1674 - 1748) who began the reform of congregational singing in England. He wrote many fine hymns - Joy to the World and O God our help in ages past are examples - and started from the principle that texts should express the religious feelings of the people. This was a total turnaround from the previously-held view that they should be scripturally based! Isaac Watts' principle holds today - I write as the General Editor of two hymn-books, both of whose editorial committees were guided by it.
Hymns followed the psalms, adapting melodies from the early chants. Catholicism developed the Canticle, lyrical portions of the Bible that were sung at specified times of worship. Canticles are a part of today's liturgy in the Roman Catholic Church. The first written chants were associated with Pope Gregory and therefore are remembered in history as "Gregorian Chants."