Several blogs of late, Mark Goodacre among others, have called attention to the YouTube musical version of the earliest Christian hymn.
“The Oxyrhynchus Hymn (P. Oxy. XV 1786) is the earliest known manuscript of a Christian hymn – dating from the 3rd century AD – to contain both lyrics and musical notation. It is now kept at the Papyrology Rooms of the Sackler Library, Oxford. The text, in Greek, poetically invokes silence so that the Holy Trinity may be praised.”
While considering early hymns, I would recommend one of my favorite books on hymns in the New Testament: Robert J. Karris, A Symphony of New Testament Hymns (Collegeville, MN: Liturgical Press, 1998).