On The Trisagion

St. Nicholas Cabasilas ca. 1319-1391

The Thrice-holy Hymn has been taken in part from the angels, and in part from Book of Psalms by the Prophet David; it was made into one hymn by the Church of Christ and dedicated to the Holy Trinity. The holy, which is sung three times, belongs to the angels (cf. Isa. 6:3), while God, mighty and immortal come from the blessed David, who says: My soul thirsts for God, the mighty, the living (Ps. 41:3). Our holy church received all this and joined the psalm with the angelic hymn and added the petition, Have mercy on us… in order to show both the harmony of the Old Testament with the New, and that angels and men form one Church and one choir. (Hieromonk Gregorios: The Divine Liturgy, A Commentary in Light of the Fathers pp. 152-153)