The first and second ward - The word which is here rendered “ward” φυλακήν phulakēn properly denotes “the act of guarding”; but it is most commonly used to denote “a prison, or place of confinement.” In this place it seems to denote the guard itself - the soldiers stationed at intervals in the entrance into the prison. These were passed silently, probably a deep sleep having been sent on them to facilitate the escape of Peter.
The iron gate - The outer gate, Secured with iron, as the doors of prisons are now.
That leadeth unto the city - Or rather into εἰς eis the city. The precise situation of the prison is unknown. It is supposed by some (compare Lightfoot on this place) that the prison was between two walls of the city, and that the entrance to the prison was immediately from the inner wall, so that the gate opened directly into the city.
Of his own accord - Itself. It opened spontaneously, without the application of any force or key, thus showing conclusively that Peter was delivered by miraculous interposition.
And passed on through one street - Until Peter was entirely safe from any danger of pursuit, and then the angel left him. God had effected his complete rescue, and now left him to his own efforts as usual.