Why did Paul go from persecuting Christians to dying for Jesus?

Paul - then called Saul - was no neutral observer. He was actively hunting Christians, approving executions and dragging believers to prison. He had status, training, and conviction invested in stamping the movement out.

Then, by his own account in our earliest written sources, the risen Jesus appeared to him on the road to Damascus. He didn't gain power or comfort; he traded everything for beatings, prison, and eventual execution. People will die for a belief they received from others, but Paul was in a position to know what he had or hadn't seen. The persecutor became a martyr because something happened he could not deny. "Last of all he appeared to me also" (1 Corinthians 15:8).