Ministering spirits, angels
And that was how the Lord’s angel found him—restful and relaxed as though he were at home in bed and the armed guard his honored guests. How the angel would tell that story when he arrived back in glory! It is generally inferred that the angel was Peter’s guardian angel. Jacob had an angel who protected him from Laban (Gen. 48:16). Daniel had an angel who protected him from the lions (Dan. 6:27). Little children have their angels who report to God’s throne any mistreatment they receive (Matt. 18:10). Paul had an angel who strengthened him when on board the sinking ship (Acts 27:23). The Holy Spirit tells us that angels are “ministering spirits, sent forth to minister for them who shall be heirs of salvation” (Heb. 1:14).
John Phillips, Exploring Acts: An Expository Commentary, The John Phillips Commentary Series (Kregel Publications; WORDsearch Corp., 2009), Ac 12:7a.