How do we know that Paul's preaching was legitimate?

Paul's preaching was validated by his encounter with Christ and supported by the testimony of Barnabas, who introduced him to the apostles. Barnabas had witnessed Paul's boldness and the authenticity of his transformation after he met Christ. It is essential in the early church to have credible witnesses, and Barnabas served as an eyewitness who testified to the change in Paul's life. Paul's fervent preaching in Damascus and later in Jerusalem demonstrates that a true conversion leads to genuine preaching of the gospel, not found merely in human tradition or learning, but through a divine revelation from Christ.