In Acts 4, Peter and John are arrested and brought before the high priest and some of his associates. In the previous two chapters Luke has described the ministry of Peter in Jerusalem on the day of Pentecost and just after that time. He and the twelve seem to have gone regularly to the temple for prayer and worship. While they were there, they had opportunity to preach Jesus as the messiah and the gospel of the risen and ascended Jesus to groups of religiously minded Jews who were also in the Temple for prayer and worship. In both cases God does a miracle which demonstrates that the messianic age has begun (the descent of the Holy Spirit and the healing of a lame man), and in both cases Peter’s sermon is based solidly on messianic prophecies found in the Hebrew Bible.
In 4:8 Peter is “filled with the Holy Spirit” as he addressed the meeting. That Peter is filled with the Holy Spirit is an indication that Luke sees this speech in the tradition of the Prophets of the Hebrew Bible. John Polhill points out that the verb used (an aorist participle of πίμπλημι) is used for “special moments of inspiration,” see Luke 1:15, 1:41, Acts 6:3-5, 7:55, for example (Acts, 143). Luke is therefore presenting Peter as giving a prophetic speech like Isaiah or Jeremiah, directly to the leadership of the Jewish people, calling even the High Priest to repent of the sin of killing the Messiah.
The words which follow are therefore a prophetic speech of condemnation, which amazes the listeners. But it is not Peter’s skills as an orator which is important, but that the words come through the Holy Spirit. In each case, the target of the speech is Jewish; 9:17 refers to Paul receiving the Spirit, 11:24 refers to Barnabas as a man “full of the Spirit.”
This “filling with the Holy Spirit” is salvation in a Pauline sense, but rather an enablement to speak boldly before a crowd of people who can (and will) physically persecute Peter for what he says in this brief speech. In what other ways is the activity of the holy Spirit evident in this chapter?