Adam Clarke on Acts 16:26

There was a great earthquake - Thus God bore a miraculous testimony of approbation to his servants; and, by the earthquake, and loosing the bonds of the prisoners, showed, in a symbolical way, the nature of that religion which they preached: while it shakes and terrifies the guilty, it proclaims deliverance to the captives, and the opening of the prison-doors to them that are bound; and sets at liberty them that are bruised.

Every one's bands were loosed - And yet so eminently did God's providence conduct every thing, that not one of the prisoners made his escape, though the doors were open, and his bolts off!