Acts 12:6-11 “And when Herod would have brought him forth, the same night Peter was sleeping between two soldiers, bound with two chains: and the keepers before the door kept the prison. 7 And, behold, the angel of the Lord came upon him, and a light shined in the prison: and he smote Peter on the side, and raised him up, saying, Arise up quickly. And his chains fell off from his hands. And the angel said unto him, Gird thyself, and bind on thy sandals. And so he did. And he saith unto him, Cast thy garment about thee, and follow me. And he went out, and followed him; and wist not that it was true which was done by the angel; but thought he saw a vision. When they were past the first and the second ward, they came unto the iron gate that leadeth unto the city; which opened to them of his own accord: and they went out, and passed on through one street; and forthwith the angel departed from him. And when Peter was come to himself, he said, Now I know of a surety, that the Lord hath sent his angel, and hath delivered me out of the hand of Herod, and from all the expectation of the people of the Jews.”
Despite his death sentence, Peter slept. The angels “smote” (struck) him to wake him. (v. 7) How could Peter rest so peacefully? Peter was sleeping with a “promise.” That promise is recorded in John 21:18, where Christ predicted that Peter would live to be an old man who needed assistance to walk. At his arrest, Peter was not an older man and still had many more years of ministry remaining. I believe he slept, knowing he had the promise of long life, and neither Herod nor any other adversary would take his life prematurely. Believers must always fight their battles and war with the promises in the Scriptures and with promises the Holy Spirit has revealed to them.