At the time it was common to identify someone with a reference to either their father or the town from which they came. Since there were many people with the name Jesus, Peter specifies that he is referring to the Jesus who came from Nazareth. He will do the same elsewhere in Acts (Acts 3:6; Acts 4:10; Acts 6:14). Nazareth was a small town at the time with around 500 inhabitants.1
22 “Men of Israel, hear these words: Jesus of Nazareth, a man attested to you by God with mighty works and wonders and signs that God did through him in your midst, as you yourselves know