In fact, just not getting involved with the entire affair would have made life much simpler for Paul. Basically, he had to turn his back on his own people and give up everything that he had and knew to spread the Gospel. So what was his motivation? As mentioned, it was a low paying job and it caused him to be a pariah among the Jews and most of the Pagans who he was ministering to.
He was clearly handpicked by God Himself to carry His message to the Gentiles ‘and’ to the Jews. Luke, not Paul, clearly and specifically documented this in Acts. He was a violent and murderous fanatical Old Covenant, Mosaic Law following Jewish Pharisee who was trained by one of the leading Jewish scholars of the time, Gamaliel. That put him as one of the upcoming men in Judaism.
He was a fire and brimstone Jew who hated Christians with a passion, thinking he was doing God's work. Then he met the risen Jesus head on, getting knocked down in the dirt and slapped along side the head. And he did a 180 in the course of a single day.
God also said that He would teach Paul what he would suffer for doing His work. And Paul did suffer. He was beaten and imprisoned, snake-bit and shipwrecked. Paul went through some rough times. In the end he was murdered by Nero.
God knew what Paul was capable of and hand picked him to be the leading missionary of all time.
