What was Saul planning to do when he went to Damascus?
Saul planned to go to Damascus to arrest any believers in Christ he could find in the synagogues and bring them back to Jerusalem for trial and punishment, often death. He had gone to the chief rulers, who could extradite Jews from foreign countries, and he acted with absolute hatred for anything contrary to Judaism.
Les explains that Saul was trying to stamp out anyone in Israel who had proclaimed Christ as Messiah, believed that, and had become separated from the mainstream of Judaism, although they were still keeping temple worship and the Law. Evidently old Saul had pretty much cleansed the homeland, and now he had gone to the chief rulers, who had enough clout with the Roman government to extradite Jews from foreign countries, such as Damascus, and bring them back to Jerusalem for trial and punishment, and more than often death. So on the road to Damascus, with that heart of absolute hatred for anything contrary to Judaism, he was trying to go to Damascus and arrest and bring back to Jerusalem for trial anybody in the synagogue he could find who were believers in Christ. Les points out that on that road to Damascus the Lord called him by grace, and if ever there was a man who didn't deserve what God did for him, it was Saul.