“For you have heard of my former life in Judaism, how I persecuted the church of God violently and tried to destroy it” (v13). In order to be heard, Paul had to remind the Galatians of the source of his spiritual authority: Jesus himself. Paul wasn’t just passing on doctrine he had heard from the apostles in Jerusalem (v11,12, 19), though he eventually met with them and gained their trust. His original experience and call were from Jesus, and Paul’s dramatically changed life was the proof.
Paul said God was “pleased to reveal His Son to me” (v16), and that encounter changed everything. Beyond simply believing, each of us can know Jesus personally by the power of the Spirit.