Persecutor Turned Promoter(Galatians 1:11-24)

Why does the apostle Paul continue to remind the church that this gospel is not from man? Why does he insist that people know that he is commissioned and called by Christ? Why does he even talk about his past life as a Pharisee compared to who he is now? Is he saying that the gospel is about him or is he making a different point? Please stayed tuned as we hear, "Persecutor turned Promoter."