"While Peter was kept in prison, the church prayed fervently for him."
It's not unexpected to read about the early church praying for someone. And it's also not unexpected that the person they're praying for (in this case, Peter) has been thrown in prison. The early Christians were repeatedly harassed and arrested because of their perceived "threat" to the Jewish community.
What was surprising, however, was what happened to Peter - God rescued him from prison in the middle of the night! Not only that, but he went straight to Mary's house (John Mark's mom) - where he knew the believers were meeting. In fact, they were praying for his release there! But when he knocked on the door, no one (except Rhoda, the maid who answered the door) believed it really was Peter!
I find it curious that the very thing they people were praying for happened - yet they couldn't believe it was possible. Wow. How often does that also happen with us? "Lord, I believe. But hep my unbelief." Amen to that.