In A New Song for an Old World: Musical Thought in the Early Church, Calvin Stapert shows how important congregational singing was to the early church as a visible and audible expression of Christian unity:
Building on Paul’s exhortation in Romans 15:5-6, Stapert asks: “Does ‘with one voice’ refer directly to singing? Probably not–at least not exclusively. But no one can doubt that it articulates a principle that the church took very seriously for her singing. The importance of singing ‘with one voice’ was a constant refrain among the early Christian writers. Listen to some of its recurrences during the first few centuries of the Christian era. Clement of Rome (ca. 96):
In the same way [as the angels] ought we ourselves, gathered together in a conscious unity, to cry to Him as it were with a single voice …
Clement of Alexandria (ca. 150-ca. 215):
The union of many in one, issuing in the production of divine harmony out of a medley of sounds and division, becomes one symphony following one choir-leader and teacher, the Word, reaching and resting in the same truth, and crying Abba, Father.
Eusebius of Caesarea (ca. 260-ca. 340):
And so more sweetly pleasing to God than any musical instrument would be the symphony of the people of God, by which, in every church of God, with kindred spirit and single disposition, with one mind and unanimity of faith and piety, we raise melody in unison in our psalmody.
Ambrose (ca. 339-397):
[A Psalm is] a pledge of peace and harmony, which produces one song from various and sundry voices in the manner of a cithara … A psalm joins those with differences, unites those at odds and reconciles those who have been offended, for who will not concede to him with whom one sings to God in one voice? It is after all a great bond of unity for the full number of people to join in one chorus. The strings of the cithara differ, but create one harmony (symphonia).”
Stapert comments: “Unity was an important matter to the early Christians, and, as these quotations show, almost from the beginning music was an expression of, a metaphor for, and a means toward unity” (25-26).