[Mary Naeem]

But why the three-fold repetition “holy, holy, holy” (called the trihagion)? The repetition of a name or an expression three times was quite common among the Jews. In Jeremiah 7:4, the Jews are represented by the prophet as saying, “The temple of the Lord” three times, expressing their intense confidence in their own worship, even though it was hypocritical and corrupt. Jeremiah 22:29, Ezekiel 21:27, and 2 Samuel 18:33 contain similar three-fold expressions of intensity. Therefore, when the angels around the throne call or cry to one another, “Holy, holy, holy,” they are expressing with force and passion the truth of the supreme holiness of God, that essential characteristic which expresses His awesome and majestic nature.