Why didn't the believers in Acts 12 believe that Peter was at the door when Rhoda said he was there?
Although they had gathered and prayed fervently for Peter's release, those believers did not actually expect God to answer. When the answer came, they could not believe it. Their response shows the same human tendency to pray repeatedly while doubting that God will really act.
Les explains that Acts 12 is a transition section, leaving Paul and Barnabas for a time and returning to Jerusalem and Peter. Peter ends up in prison, and Jewish believers are having a prayer meeting at the home of one of the believers, praying for his release. When the angel opens the prison doors and escorts Peter to the street, Peter stands at the gate of that home. A young lady goes out, sees who it is, does not let him in, and runs back to tell those in prayer that Peter is at the door. Did they believe it? No. Les points out that they had been praying fervently for his release, yet when it happened they could not believe it. He says people then are no different than people today: we pray and pray, but most of the time we really do not believe it is going to happen. Yet God is a prayer-answering God.