This is probably the strongest argument for proof of the resurrection. The changed lives of the disciples prove that Jesus resurrected. At the death of Christ, the disciples fled puzzled because they were expecting Jesus to be their new political ruler to overtake Rome, yet later after the resurrection, they were empowered with the Holy Spirit to be bold witnesses of this resurrection. (Matt 28:19, Acts 2:4) They went out and turned the world upside down (Acts 17:6). At their first outreach, Peter stood up with boldness and preached to thousands. (Acts 2: 14–41) Being eyewitnesses brought them assurance of the reality of the resurrection and it also brought them confidence to step out by faith into the opposition that the religious rulers had waiting for them.
As you witness to your friends, be sure to use your own personal testimony telling them how God changed your life. No one can argue about what God has done in your life.
In Acts 26, King Agrippa could not argue with Paul about what God did in Paul’s life. King Agrippa’s only response was, “In a short time you will persuade me to become a Christian.”