Why was Paul sent from Jerusalem to Tarsus?
The brethren in Jerusalem, when they found out that the unbelieving Jews were about to kill him, brought him down to Caesarea and sent him forth to Tarsus. This allowed him to return to his home city and begin his ministry.
Les explains that the brethren in Jerusalem—Barnabas and probably some other Jews—acted when they learned the unbelieving Jews were about to kill Paul. They brought him down to Caesarea, a seaport, and sent him forth to Tarsus, his home city, where he began his ministry. This followed his three years at Sinai and two weeks with Peter in Jerusalem. Les also notes Paul customarily went first to the synagogue of the Jew, then to the Gentile when rejected.