‘But an angel of the Lord by night opened the prison doors, and brought them out, and said, “Go all of you, and take your stand and speak in the temple to the people all the words of this Life.” '
But that night the angel of the Lord opened the prison doors and brought them out, and commanded them to go into the Temple and defiantly ‘take their stand' (aorist passive participle) and proclaim ‘the words of this life' i.e. the ‘life' connected with the resurrection, the eternal life that they were proclaiming. There is only one explanation for this. It was to be a deliberate act of passive defiance. Note how there is nothing here, apart from the act itself, which is seen as dramatic or the fantastic. It is stated quite openly and baldly. It is the fact that matters not the ‘miracle'.
‘An angel of the Lord.' The use of this term is very distinctive in Acts. It very much emphasises the personal intervention of God, as it does in the Old Testament. See Acts 7:30; Acts 8:26; Acts 12:7; Acts 12:23. How He did it is another matter. He may well have used a human instrument who was sympathetic to the Apostles and had access to the keys. But the impression that Luke wants to give is that God Himself intervened.
In a sense this incident seems unnecessary. Why open the gates of the prison and send them back, only for them to be rearrested? The answer is in fact simple. This was a bold statement of the presence of the new age. It had been a promise of God that when His Servant and His Anointed came He would deliver the captives from prison (Isaiah 42:7; Isaiah 49:9; Isaiah 61:1; Zechariah 9:11 compare Psalms 69:33; Psalms 142:7) and would tell them to show themselves (Isaiah 49:9). And that is what He was doing here. It was a typical acting out of prophecy.
It was also a confirmation to them that what they were doing was right. They had no business in prison. Their business was out side preaching the word of life.
Furthermore it would be a reminder to prisoners of God in the future that no Christian ever languished in prison without God knowing. He would only be there while God permitted it. Some would be released, others would die there, but all would know that God could have released them whenever He would. They were therefore the Lord's prisoners, and safe in His hands.