Emphasizing the contrast with v. 18. The authorities imprisoned the apostles, the angel released them. It would seem as though this was a divine protest against the actions of the Sadducees, who taught that there was “neither angel, nor spirit” (ch. 23:8).
Angel.
Luke is obviously recording what he considers a supernatural occurrence. Those who do not accept that view, and who yet wish to maintain the historicity of the narrative, are driven to suggest that the “angel” was some zealous and courageous disciple; and that the apostles, in the darkness of the night and the excitement of their liberation, mistakenly ascribed their rescue to the intervention of an angel. But there is no possibility of adequately explaining Luke’s words in any other terms than a miraculous deliverance. The human aid of Gamaliel, at a later hour, is freely and openly recorded (vs. 34-39). But here the aid is frankly described as supernatural. Although the apostles were arrested again only a few hours later (v. 26), God had demonstrated His power, the apostles had the comfort of heavenly intervention on their behalf, and the Sadducees had been given an opportunity to know that they were fighting against supernatural powers. Surely the angels are “ministering spirits, sent forth to minister for them who shall be heirs of salvation” (Heb. 1:14).
By night.
Rather, “during the night.”
Opened the prison doors.
Doors, even the firmly fastened doors of prisons, are no problem to the angels of God. The apostles were taken out from under the very eyes of the keepers, either under the cover of deep darkness or because the eyes of the guards were “holden” (cf. ch. 12:6, 7). The doors were left secured, or were locked again, leaving everything as it had been before the angel came (cf. ch. 5:23).