Why was Paul glad when the believers who confessed Jesus as Messiah were condemned to death?
Paul was glad because he sincerely believed he was doing God a service. He viewed the believers in Jesus as imposters and blasphemers who opposed the Old Testament religion. His zeal for Judaism led him to vote against them and approve their execution, thinking he was removing false teachers from Israel.
Les explains that Paul was a Judaizer completely wrapped up in Old Testament religion, and such religious zeal made him ready to kill anyone who opposed him. Paul says in Acts 26:9-11 that he thought he ought to do many things contrary to Jesus of Nazareth, shut up many saints in prison, and when they were put to death, he gave his vote against them. He was glad to see them condemned because he thought he was doing God a service, viewing them as imposters and blasphemers. This was the persecution that arose about Stephen, and Saul was consenting unto his death, even pursuing Jewish believers to Damascus.