Peter often emphasizes the role of the apostles as witnesses to the good news (the message about Jesus’s life, death, and resurrection). He reminds his listeners that they had direct contact with Jesus.
The apostles ate and drank with Jesus after he rose from the dead (see Luke 24:41–43). They saw him alive again. Because they were eyewitnesses of his resurrection, they could testify that Jesus had defeated death (see Acts 3:15; 4:33; 13:30–31).
Jesus chose the original apostles ahead of time to be his witnesses (see 1:12–26). Later, others continued this work. For example, Paul and Barnabas preached and taught in the name of Jesus Christ (see 9:15; 14:1–3; 26:16).