But the angel of the Lord by night opened the prison doors, and brought them forth, and said, But the angel of the Lord - opened the prison doors - This was done:
1. To increase the confidence of the apostles, by showing them that they were under the continual care of God; and,
2. To show the Jewish rulers that they were fighting against Him while persecuting his followers, and attempting to prevent them from preaching the Gospel.
This was another warning graciously given them by a good and merciful God, that they might repent, and so escape the coming wrath.