Acts 4:1-4 - They were greatly disturbed

4:1,2

The preaching of Peter and John upset the religious leaders. This was not because it was illegal in itself to preach in the  temple courts, but because of what they were preaching. The Sadducees in particular would be disturbed by the centrality of the resurrection in their preaching, as they did not believe in the resurrection, unlike the Pharisees. All of them would be concerned about their preaching that Jesus was raised from the dead. We need to realise that the gospel is inherently offensive to the world.

4:3,4

They seized Peter and John. Clearly Peter and John were recognized as leaders of the church. They put them in jail after arresting them, as it was evening it was not possible to hold a “trial” at that time. Notably, this did not seem to concern them when Jesus was arrested.  So we have here the reaction of the religious authorities (who also had a significant civil authority as well). However, that was not the only reaction. “Many who heard the message believed”. Unlike in John’s gospel, “believed” seems to be a stronger description in Acts. So at this point the number of men who believed was about five thousand. Now to our modern ears the limiting of the number to the number of men may offend us. However, we need to remember that Luke was writing for the first century, not the twenty first century. So stating that a significant number of men believed indicated that the gospel was truly having an effect. They would naturally assume that a similar number of women also believed.