What was Paul doing among the Gentile cities as he preached the gospel?
As Paul traveled among Gentile cities, he preached the gospel and by that preaching was calling out a people for the name of Christ. He repeatedly defended his apostleship and endured continual suffering so that the Gentiles could receive the message of grace.
Les teaches that Paul went out amongst the Gentile cities and, by virtue of preaching the gospel, was calling out a people for the name of Christ. Because Jews—whether believing or still in Judaism—constantly attacked him, saying he never walked with Jesus like Peter did, Paul had to defend his apostleship. Over and over he referred to how he had suffered and suffered and suffered some more so that the Gentiles could get this message of grace. This is basically the whole theme of the first six chapters, showing the Corinthians all he had to go through for the sake of the gospel. Judaizers followed in Paul's footsteps, telling his converts they could not be saved on Paul's gospel alone but still had to practice Judaism, be circumcised, and keep the law. That just about drove the apostle up the wall, and so he suffered because of that.