Isaiah 6:3

Holy, holy, holy - This hymn performed by the seraphim, divided into two choirs, the one singing responsively to the other, which Gregory Nazian., Carm. 18, very elegantly calls Συμφωνον, αντιφωνον, αγγελων στασιν , is formed upon the practice of alternate singing, which prevailed in the Jewish Church from the time of Moses, whose ode at the Red Sea was thus performed, (see Exodus 15:20 , Exodus 15:21 ;), to that of Ezra, under whom the priests and Levites sung alternately,

"O praise Jehovah, for he is gracious;

For his mercy endureth for ever;"

Ezra 3:11 . See De Sac. Poes. Hebr. Prael. xix., at the beginning.