Why was Paul persecuting the church? I've always assumed it was because they were worshiping Jesus. No, its because they were advocating against circumcision.
13 You have heard, no doubt, of my earlier life in Judaism. I was violently persecuting the church of God and was trying to destroy it. 14 I advanced in Judaism beyond many among my people of the same age, for I was far more zealous for the traditions of my ancestors.
21 Then I went into the regions of Syria and Cilicia, 22 and I was still unknown by sight to the churches of Judea that are in Christ; 23 they only heard it said, “The one who formerly was persecuting us is now proclaiming the faith he once tried to destroy.” 24 And they glorified God because of me.
2 Listen! I, Paul, am telling you that if you let yourselves be circumcised, Christ will be of no benefit to you. 3 Once again I testify to every man who lets himself be circumcised that he is obliged to obey the entire law. 4 You who want to be justified by the law have cut yourselves off from Christ; you have fallen away from grace.
The persecutions wasn't for faith in Christ, the persecution was for opposition to circumcision. It is well known that Jews did persecute those who advocated against circumcision. But in Gal 2 Paul says that James was okay with his gospel. However, were talking about a split here between Gentile and Jewish.Gal 6:
12 It is those who want to make a good showing in the flesh that try to compel you to be circumcised—only that they may not be persecuted for the cross of Christ.
The issue was that other Jewish officials, the Pharisees to which Paul belonged, were not okay with this. Gentiles lived in Judea, there were plenty of them. Apparently James' church wasn't including the Gentiles or was telling them to get circumcised, in order to avoid persecution. There was evidently other churches, not associated with James, who were also advocating against circumcision prior to Paul. It is those churches that Paul was persecuting prior to his conversion.
Paul is calling out James, saying, that he and his group, "try to compel you to be circumcised—only that they may not be persecuted for the cross of Christ."
And Paul has been saying hey, I used to persecute people for not getting circumcised too, but now I'm standing up against circumcision. I don't care if I get persecuted for telling you that you don't need to be circumcised. I'm a better apostle than James and the others because I'm willing to suffer persecution to stand up against circumcision.
The persecution had nothing to with with Jesus.