Most pure feast, have mercy on us. Food of Angels, have mercy on us. Hidden manna, have mercy on us. Memorial of God's wonders, have mercy on us. Super substantial Bread, have mercy on us.
Elsewhere in Luke 1, the title "Lord" refers to God, e.g. "an angel of the Lord" [Luke 1:11]. It should be noted that the name YHWH, being too sacred, could not be uttered, so the Hebrews said ...