Paul did not persecute the church... at least not while he was named "Paul". He persecuted the church while he was called Saul of Tarsus, a rising young star among the Jewish ruling classes. He took the lead in persecuting the church and was responsible for the execution of Stephen.
He continued in his zealous hatred and persecution of the church until he was converted by his encounter with the glorious risen Christ on the road to Damascus as recorded in Acts chapter 9. He then changed from being the leader of the persecutors to being the most effective preacher of the Gospel. It was only then that his name was changed from "Saul of Tarsus" to Paul the Apostle.
I hope you have found this helpful.