Evidence suggests that the Greek text of "Let All Mortal Flesh" may date back to the fifth century. The present text is from the Liturgy of St. James, a Syrian rite thought to have been written by St. James the Less, first Bishop of Jerusalem. It is based on a prayer chanted by the priest when the bread and wine are brought to the table of the Lord. (https://hymnary.org/text/let_all_mortal_flesh_keep_silence)
Gerard Moultrie's translation from Greek was arranged by Ralph Vaughan Williams to the tune "Picardy", a French medieval folk melody. (https://en.wikipedia.org/wiki/Let_all_mortal_flesh_keep_silence)
Let all mortal flesh keep silence,
And with fear and trembling stand;
Ponder nothing earthly minded,
For with blessing in His hand,
Christ our God to earth descending
Comes our homage to demand.
King of kings, yet born of Mary,
As of old on earth He stood,
Lord of lords, in human vesture,
In the body and the blood;
He will give to all the faithful
His own self for heavenly food.
Rank on rank the host of heaven
Spreads its vanguard on the way,
As the Light of light descendeth
From the realms of endless day,
Comes the powers of hell to vanquish
As the darkness clears away.
At His feet the six winged seraph,
Cherubim with sleepless eye,
Veil their faces to the presence,
As with ceaseless voice they cry:
Alleluia, Alleluia
Alleluia, Lord Most High!
