Isaiah 6:3

(3) And one cried unto another.—So in Psalms 29:9, which, as describing a thunderstorm, favours the suggestion that the lightnings were thought of as the symbols of the fiery seraphim, we read, “in his temple doth every one say, Glory.” The threefold repetition, familiar as the Trisagion of the Church’s worship, and reproduced in Revelation 4:8 (where “Lord God Almighty” appears as the equivalent of Jehovah Sabaoth), may represent either the mode of utterance, first antiphonal, and then in full chorus, or the Hebrew idiom of the emphasis of a three-fold iteration, as in Jeremiah 7:4; Jeremiah 22:29. Viewed from the standpoint of a later revelation, devout thinkers have naturally seen in it an allusive reference to the glory of Jehovah as seen alike in the past, the present, and the future, which seems the leading idea in Revelation 4:8, or even a faint foreshadowing of the Trinity of Persons in the Unity of the Godhead. Historically we cannot separate it from the name of the Holy One of Israel, which with “the Lord of hosts” was afterwards so prominent in Isaiah’s teaching.