Acts 12:7

And behold, the[an] angel of the Lord came upon him The verb is the same which is used (Luke 2:9) of the angel appearing to the shepherds. The idea conveyed is that the heavenly visitor appeared over those to whom he was sent. The passage just quoted continues "and the glory of the Lord shone round about them," words which are strikingly parallel with this description of St Peter's release, "and a light shined in the prison."

in the prison The word is not the same as in the last verse. To make the distinction clear read here "cell" or "chamber." The light was due to the presence of the angel who came with the glory of the Lord.

and he smote Peter on the side, and raised him up Rather, roused him up. The verb indicates that he awoke him from his sleep, but not that he helped him to arise.