What does Acts 4:13 mean?

"Uneducated" is from the Greek root word agrammatos and "common" is from the Greek root word idiōtēs. Together, they mean Peter and John had no formal training in rhetoric or Jewish theology. Culturally, it shows the deep disrespect groups like the Sanhedrin had for "lesser" people. Peter and John are not members of a privileged class that could afford higher education, nor are they of a religious class that would sit under a scholar. In fact, they are fishermen (Mark 1:16–20), and Jesus, their rabbi, didn't have formal education, either (John 7:15). And yet, not only does Peter have the confidence to present his case before the highest religious court of the land (see Mark 1:21–22), he has the audacity to place Jesus into Old Testament passages as if he were a rabbi schooling the chief priests and scribes.

Peter and John are able to speak so confidently because of their training under Jesus and the empowerment of the Holy Spirit. They are following the example of Jesus, who spoke with an authority that the teachers in the synagogue dared not assume (Mark 1:27). They are obeying Jesus, acting as His witnesses in Jerusalem (Acts 1:8). And they are saying the words the Holy Spirit gives them, as Jesus promised (Matthew 10:19–20).

Peter's boldness is even more notable. John, at least, knows the high priest (John 18:15). Peter cut off the ear of the high priest's servant (John 18:10) and once denied knowing Jesus, possibly out of fear that the servant's friends and relative would recognize him as the assailant (John 18:26–27).

With the indwelling of the Holy Spirit, Peter can boldly talk about Jesus in front of any audience (Acts 2:1–4). The Holy Spirit gives him both the words to say and the courage to say them. Later, Paul will explain, "God chose what is foolish in the world to shame the wise; God chose what is weak in the world to shame the strong; God chose what is low and despised in the world, even things that are not, to bring to nothing things that are, so that no human being might boast in the presence of God" (1 Corinthians 1:27–29). And God can choose an uneducated fisherman who is guilty of assault to teach the Jewish leaders their own theology and accuse them of murdering an innocent One.