1. Hebrews 1.13-14
And to which of the angels has God ever said, “Sit at my right hand until I make your enemies a footstool for your feet”? Are they not all ministering spirits sent out to serve for the sake of those who are to inherit salvation?
Angels, like the Blues Brothers, are on a mission from God. They are the envoys of the Most High: the Greek word angelos literally means “messenger,” and indeed what we most often see angels doing is bringing glad tidings (think of the Christmas gospel from Luke 2).
Hebrews 1 also tells us that the prime directive of the angels is to serve the elect: their job is to look after God’s people. This moves us toward the general notion of angels as guardians, but not to individually-assigned “guardian angels.”
2. Psalm 91.11-12
For he will command his angels concerning you to guard you in all your ways. On their hands they will bear you up, lest you strike your foot against a stone.
Psalm 91 gets us closer. The “you” throughout these verses is singular: God’s angels are commanded to care for you—yes, you! (Satan takes the “you” to mean Jesus in Matthew 4.)
I suspect that Luther was drawing on this when he included in his Morning and Evening Prayers in the Small Catechism, “Let your holy angel be with me, that the evil foe may have no power over me.” Luther, at least, didn’t seem to shy away from the notion of an angel guarding him.
3. Matthew 18.10
“See that you do not despise one of these little ones. For I tell you that in heaven their angels always see the face of my Father who is in heaven.”
In the context, “little ones” refers to Jesus’ disciples. Thus, we are given the impression that an angelic protector is assigned to each of God’s children: “their angels.” This would seem to fit with the verses from Hebrews and Psalms as well.
So let's put together what we have learned. Angels are 1) servants of God that 2) protect His people 3) individually as well as corporately. It’s as though God gives gracious spies on behalf of His people. Sounds like guardian angels to me!
To be sure, a guardian angel is no replacement for the Holy Trinity. It is not someone to be prayed to or even looked to in times of trial since they’re creatures like ourselves. I will admit, though, that I rest a little easier thinking that my Heavenly Father’s mercy is so bountiful that He would enroll even further care for me.
Others may disagree with this interpretation, and that’s fine; angels are securely on the outer reaches of fundamental Christian doctrine. But take this occasion to heed the Psalmist: “Bless the Lord, O my soul, and all that is within me, bless his holy name! Bless the Lord, O you his angels, you mighty ones who do his word, obeying the voice of his word!”