Imagine you are Saul of Tarsus, doing everything you can to destroy the name of Jesus of Nazareth, and as you travel to the city of Damascus to persecute the disciples of Jesus there, this happens, as related by Saul himself,
“Now it happened, as I journeyed and came near Damascus at about noon, suddenly a great light from heaven shone around me. And I fell to the ground and heard a voice saying to me, ‘Saul, Saul, why are you persecuting Me?’ So I answered, ‘Who are You, Lord?’ And He said to me, ‘I am Jesus of Nazareth, whom you are persecuting’” (Acts 22:6-8).
How would you react to hearing such words? Saul had to have been shocked deeply. He had believed Jesus to be a fraud, but then discovered that Jesus of Nazareth is the Christ, making Him the Son of God, and Saul had devoted his life to destroying that very name.
Once he knew the truth, perhaps we can understand his unquenchable zeal.