The subject of this article is the earliest notated Christian hymn, dedicated to the Holy Trinity (Papyrus Oxyrhinchus No1786, 3 c. AD). This manuscript could have been used for choir chanting. Its lyrics dominate over music. Its musical text is connected not only with the genesis of Gregorian chant, but also with the earliest stage of the genesis of the hymnographic canon. In its structure and composition the poetical text is close to early monodia, i.e. to compositions connected with the Ode of Three Children. At first its strophes could be refrains to the verses of the Ode of Three Children, then it became an independent Morning Hymn, like Gloria in Excelsis. One can find many parallels between these two hymns and those of Melito of Sardes and Auxentius of Bithynia.