Who is the angel of the Sacrifice?
The Angel of the Sacrifice is the angel referred to when the priest states, "O angel of this offering who ascends to the highest with this praise, remember us before the Lord that He may forgive us our sins." The Orthodox, faithful believes that there is an angel present for the sacrifice who departs at the end of the Divine Liturgy carrying our prayers to heaven.
The dismissing of the angel of Sacrifice occurs following the Thanksgiving Prayer after the Holy Communion. The deacon pours some water into the hands of the priest who then breathes three times on the water while drawing the sign of the cross with his head. Subsequently, the priest stands before the altar and dismisses the Angel of Sacrifice by sprinkling some of the water on the altar and the rest upward saying "O angel of this offering............."
It is worth noting that neither the priest nor the deacons are allowed to take off the vestments of service; and the congregation should not depart before the angel of the Sacrifice is dismissed.