Why did Paul leave Jerusalem for Tarsus?
Paul left Jerusalem for Tarsus because the brethren discovered that unbelieving Jews were about to kill him. They brought him to Caesarea and sent him to Tarsus, his home city, where he began his ministry, after having spent three years at Sinai and two weeks with Peter in Jerusalem.
Les explains that when the brethren—Barnabas and probably some of the other Jews in Jerusalem—learned that the unbelieving Jews were about to kill Paul, they brought him down to Caesarea and sent him forth to Tarsus. From Caesarea, a seaport town, he went up to the area of his home city of Tarsus and began his ministry. Les notes that Paul always went first to the synagogue of the Jew, but when they rejected him, he would go to the Gentile. Later, when the church at Antioch showed signs of Gentile interest, Barnabas, led sovereignly by the Holy Spirit, went to Cilicia, into the area of Tarsus, to look for Saul. He found him and brought him back to Antioch, where Gentile Christianity began to flower and the believers were first called Christians.
Which when the brethren knew, they brought him down to Caesarea, and sent him forth to Tarsus.