In the year that King Uzziah died (c. 740 BC), Isaiah saw the Lord seated upon a throne, high and lifted up, with the train of His robe filling the Temple. Above Him stood the seraphim, each with six wings — two covering the face, two covering the feet, two for flying — and they called to one another and said: 'Holy, holy, holy is the LORD of hosts; the whole earth is full of his glory.' The foundations of the thresholds shook at their voices, and the house was filled with smoke.
Isaiah cried out: 'Woe is me! For I am lost; for I am a man of unclean lips.' One of the seraphim flew to him with a burning coal taken from the altar with tongs, touched it to his lips: 'Behold, this has touched your lips; your guilt is taken away, your sin forgiven.' Then the LORD asked: 'Whom shall I send? Who will go for us?' Isaiah answered: 'Here am I; send me.' The Trisagion ('Holy, holy, holy') has been part of the eucharistic Sanctus of every Christian liturgy since the earliest centuries.