But Peter continued knocking: and when they had opened [the door], and saw him, they were astonished.
Note 14 at Ac 12:16: Just as Peter was denied access to Mary's house because they couldn't believe, so we deny the Lord access into our lives because of our unbelief. The disciples were praying for just such a thing as what happened, but they didn't really have the faith to believe it. Likewise, we pray for God's power, but when it comes, we can't believe it. Praise God that, like Peter, the Lord keeps on knocking (Re 3:20).