Heavenly Liturgy: Hymns of the Seraphim, Eternal Praise, Liturgy as Icon

"The words of the Sanctus come from the Seraphim. 

In this hymn the language of the liturgy 

is not simply modeled on celestial worship, 

it actually uses the same words 

as the heavenly liturgy. 

Not all the words of the liturgy, however, can make such a claim. 

Yet most are taken from the Scriptures. 

I have already mentioned several parts of the liturgy drawn directly from the Bible, 

for instance, the Kyrie Eleison and the Agnus Dei; 

but let me illustrate the point 

by reference to one of the ancient liturgies of the Church, 

the Liturgy of St. James used at Jerusalem and other places in Palestine and Syria

. . .Again and again in their comments on the Hymn of the Seraphim, 

the Church Fathers speak of what Isaiah "heard" or "saw" 

or what was "handed over" to us by the Seraphim. 

So let us allow the historical critics to pursue their theories 

about where John got his information about the Holy, holy, holy 

being sung in heaven and consider the vision itself. 

If the accounts in Isaiah 6 and Revelation 4 

are viewed in their own terms,  

that is as visions, 

they give us a precious insight into Christian worship. 

Some of the words we use in the Liturgy, 

in this case the words of the Sanctus, 

are not human words crafted by mortals. 

They are words on loan 

from Angels and Archangels, Cherubim and Seraphim 

and are to be treated with reverence."

excerpt from
Angels and Archangels: The Worship of Heaven and Earth,
by Robert Louis Wilken Read more here