Holy, Holy, Holy! is a Christian hymn written by Reginald Heber (1783–1826). Its lyrics speak specifically of the Holy Trinity, having been written for use on Trinity Sunday. It quotes the Sanctus of the Latin Mass, which translated into English begins "Holy, Holy, Holy! Lord God of Hosts". The text also paraphrases Revelation 4:1-11. John Bacchus Dykes composed the tune Nicaea for this hymn in 1861. The tune name is a tribute to the First Council of Nicaea which formalized the doctrine of the Trinity in 325.