Who is "your holy angel" in Luther's prayer? I notice that it isn't capitalized, but they must have power over "the wicked foe," who I assume is Satan.
The holy angels are those angels who did not join in with Satan (“the wicked foe”) and other angels in rebelling against God (2 Peter 2:4). The holy angels are “ministering spirits sent to serve those who will inherit salvation” (Hebrews 1:14). The holy angels carry out God’s command “to guard you in all your ways” (Psalm 91:11). The “holy angel” in Martin Luther’s prayers references any of the heavenly host whom God might choose to use to carry out his good and gracious will in our lives. Might God use a single angel on occasion? Yes. Might he use more than one angel on occasion? Yes.
The Bible does not state specifically that God has assigned a guardian angel to each Christian. While it would be comforting to know that God has matched one angel to us for life-time service and protection, it is even more comforting to know that God employs angels—plural—in his providential care of each Christian.
God’s gracious use of angels in our lives provides another reason for praising God. “Lord God, to you we all give praise; To you our joyful hymns we raise That angel hosts you did create Around your glorious throne to wait. But watchful is the angel band That follows Christ on ev’ry hand To guard his people where they go And break the counsel of the foe. O Lord, awaken songs of praise For angel hosts that guard our days; Teach us to serve you and adore As angels do forevermore.” (Christian Worship 196:1, 5-6)