In trying to discern some of the truth about the phenomenon of Orthodox sacred music, it helps to start at the beginning. Where does sacred music begin? For Orthodox Christians who with a simple faith accept the authority of Holy Scripture and Holy Tradition, the true origin of sacred music is not to be discovered in ancient liturgical manuscripts or in passing references to psalmody in the New Testament and early Fathers, but is to be found in the singing of the angelic choir, those first-created beings who have been chanting fitting praises to God since before the beginning of the visible creation.
Herein, according to the witness of Scripture and the Saints throughout the ages, lies the archetypal pattern of sacred music. It is as a participant in the angelic singing that mankind — by virtue of Christ’s Incarnation, whereby ‘the things of earth join chorus with the heavens,  — becomes able once again to offer right worship (orthodoxia) to the Creator in purity of heart. I suggest, therefore, that we use the singing of the angels — and, specifically, three essential characteristics of it — as a starting point for our ‘small entrance’ into understanding the phenomenon of Orthodox sacred music.
One essential characteristic of angelic song that is evident in Scripture is that the music of the angels is exclusively vocal, that it is sung in some manner, usually with discernible words, and that it is thus a direct musical offering of the angels’ bodily and rational nature (according to the angelic sense of a ‘body’ ).
The popular Western concept of angels accompanying their singing with harps and other instruments is unknown in Scripture and Orthodox tradition.  This is important because, in exclusively singing the praises of God, the angels offer Him something essential to themselves rather than making an offering by way of a medium extrinsic to their nature. This is one key reason why Orthodox Christian liturgical tradition (including that of the West, until the Middle Ages) does not permit the use of musical instruments in the divine services…
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