While Peter is in prison, people were gathered at Mary’s home praying. Mary is the mother of John Mark, and her home appears to be the location of a house church. Her husband is not mentioned so she may be another wealthy widow who supports a local church (like Tabitha, for example). John Mark may have some role as a leader in the church along with Peter. The evening that Peter is rescued, this community is gathered to pray.
What Luke does not tell us is what were they praying for. It is possible that this is simply a meeting of a house church for a prayer time. It is the Passover, so it is possible that these Jewish believers gathered at Mary’s house to share a Passover meal and then spend time in prayer after the meal. But given the context it is reasonable to assume that they were praying for Peter.
However, if they were praying for his release, then their response to Peter’s escape from prison is unusual. When Peter knocks at the door the servant Rhoda is so overjoyed that Peter is at the door she forgets to let him in to the house! When she reports that Peter is at the door the people gathered to pray think that she is “out of her mind” (μαίνομαι, literally, “you’re crazy”). They even suggest that she has seen “Peter’s angel.” Neither response sounds like they expected God to answer a prayer to rescue Peter.
John Polhill thinks that this might be a reference to the Jewish belief in guardian angels, or perhaps spirits of the recent dead who lurk for a time after death. Polhill cites Tobit 5:4-16, although this is not exactly the same sort of situation (Acts, 282) . Even when Peter finally gets into the house, the whole group is amazed by this escape. If they were praying for escape, they seem rather surprised by it.
It is more likely that the gathered church was praying that Peter would actually die for his faith and not deny Christ. It must have been well known by this point that Peter and the twelve all once denied Christ. Peter’s denial was most spectacular, denying his association with Jesus three times soon after he declared his loyalty to Jesus. With the apostle James dead, perhaps this group is worried that Peter will not be able to withstand the pressure and he will deny that Jesus was in fact raised from the dead. A denial of this sort would be a disaster for the Jewish Church in Jerusalem.
This story underscores the importance of fa faithful witness in Acts. The gathered believers want Peter to be that faithful witness, willing to continue to declare his faith even if he pays with his life. Peter is a changed man after the resurrection and he has already stood up to the Sanhedrin on several occasions.
This story demonstrates that faithful witness may be required not simply to live for Christ, but also to die for him.