Stephen is accused of blasphemy against the Law and the Temple, he defends these accusations by calling his accusers to surrender their heart to the new work that God is doing through the resurrection.
The Apostles Peter and John stare in the face of the men that ultimately had Jesus killed and stick to their story, knowing full well that they were risking their own lives. After encountering the resureciton there is no alternative: proclaim what you've seen.
In Acts 4 a story of healing and an imperative to turn from sin are paired together. We are reminded that turning away from something isn't enough: what are we turning toward?
The result of the Resurrection was a community that looked and acted differently. Acts 2 shows us some valuable hallmarks of that new movement, halmarks that should be a challenge us to go deeper into our commitment to live the Gospel.
In the second half of Acts 2 Peter delivers his famous Pentecost sermon. He focuses on complicity of the gathered Jews in the execution of Jesus, and the world changing power of the resurrection.