And at midnight Paul and Silas prayed, and sang praises unto God: and the prisoners heard them.
Note 3 at Ac 16:25: It is certain that Paul and Silas didn't feel like praying and singing praises unto God (see note 2 at Ac 16:24). They were going directly against all their natural feelings and deliberately exercising their will to enter into praise. This is the way that we abound in faith (Col 2:7), and a supernatural deliverance was the result. If we praise by faith instead of complaining through pain, we will experience God's miraculous power too. If they could do it, so can we (Col 1:12).
Note 4 at Ac 16:25: Special mention is made of the prisoners hearing Paul and Silas praying and singing praises unto God. This explains why none of the prisoners escaped when the earthquake came and their prison cells were opened. They had apparently been moved by Paul and Silas' demonstration of joy and faith to such a degree that they recognized the earthquake as a direct intervention of God and followed Paul and Silas' leading in not fleeing the prison. This was as great a miracle as the earthquake itself.