Orphaned in his childhood,
Cosmas was adopted by the Syrian father of
Saint John of Damascus.
Cosmas and his brother by adoption, John, are said to have been educated together by an elderly monk. Subsequently the two young men left
Damascus to enter the Monastery of Saint Sabas, near Jerusalem. In 743,
Cosmas became
bishop of Majuma, Palestine (near
Gaza City).
Cosmas was to be remembered as a great ecclesiastical poet, many of whose compositions became a permanent part of the Byzantine liturgy. For example, the sixth, seventh, eighth, and ninth "odes" used for the Byzantine Rite's
Holy Saturday office of Orthros (the eastern equivalent of Matins, the first "hour" of the Divine Office) are attributed to Cosmas. These texts express awe in contemplating the humble entombment of the Son of God, depicting Christ's death and burial as a triumph over death and hell: "Truly,
hell was pierced and destroyed by the divine fire when it received in its heart him who was pierced in his side with a spear for our salvation." The ninth "ode" constitutes a dialogue between
Christ in death and his grieving Mother.