Acts 4 is a witness to the missional beliefs of Peter and the earliest Christians, and to helps u in this reading, we are reading The Acts of the Apostles (Abingdon New Testament Commentaries). After Peter witnesses to the resurrection-shaped gospel, we read this in Acts 4:13-22:

When they saw the
courage of Peter and John and realized that they were unschooled,
ordinary men, they were astonished and they took note that these men
had been with Jesus. But since they could see the man who had been healed standing there with them, there was nothing they could say. So they ordered them to withdraw from the Sanhedrin and then conferred together. “What
are we going to do with these men?” they asked. “Everybody living in
Jerusalem knows they have done an outstanding miracle, and we cannot
deny it. But to stop
this thing from spreading any further among the people, we must warn
these men to speak no longer to anyone in this name.” Then they called them in again and commanded them not to speak or teach at all in the name of Jesus. But Peter and John replied, “Judge for yourselves whether it is right in God’s sight to obey you rather than God. For we cannot help speaking about what we have seen and heard.”

After
further threats they let them go. They could not decide how to punish
them, because all the people were praising God for what had happened. For the man who was miraculously healed was over forty years old.

One of the great lines I read in Jimmy Dunn’s little commentary on Acts was that God’s Spirit empowers humans to transcend human limitations and to transform human inabilities. This is what we see with Peter: his lack of a formal education (probably in a proto-rabbinic direction) is overcome by his power of rhetoric to witness to the saving work of God in the resurrection of Jesus Christ.

God’s Spirit empowers us to do missional work in ways we did not know possible. That’s the point.

What the opponents of the gospel of resurrection observed is telling: they saw that they had been with Jesus, which can be interpreted in myriad of ways. I recommend we leave it simple and general: they saw that they were Jesus-shaped people.

Spirit-empowered and resurrection-shaped witness is fearless: Peter, unable to do anything but tell the truth of Jesus, witnesses to the gospel of Jesus Christ even if the authorities tell him not to.