The persecution, sparked by Stephen's religious murder, was effective in driving many Christians out of Jerusalem (Acts 8:1).  But that was all part of God’s plan … because they took the gospel with them: many more people came to believe in Jesus because of Philip's ministry in Samaria and Judea (Acts 8:4-40).  But Saul (later called Paul, the Apostle), who was present when Stephen was stoned by the Sanhedrin, then wanted to eliminate all those who believed in Jesus (then called 'people of the Way') (Acts 22:19-20).

Saul wrongly believed that God had called him to root out and punish anybody who believed in Jesus, even in foreign countries (Acts 26:9-11).  Religiously ambitious, perhaps he wanted to prove his devotion to more senior clerics; maybe they might appoint him to the Sanhedrin.  So, he asked the high priest for permission to chase the new Christians (who still went to synagogues) to Damascus in Syria.  He intended to bring them back to Jerusalem on a charge of blasphemy (Acts 6:11-12).

But the Lord had other plans.  He had not sent Saul to destroy the church, but to help Him build it.  Saul had believed a lie (Galatians 1:13) and the Lord Jesus confronted him personally. A very bright light stopped him.  Dazzled, he fell to the ground; and then Jesus spoke.  He knew Saul's name; He knew what Saul had been doing; He identified Himself with His persecuted people so that their suffering was His concern.  He asked Saul the simple question: "Why are you persecuting me?"

Religious passion is good, but only if it is directed by the Lord.  Otherwise, it is foolishly dangerous.  Divinely unauthorised spiritual fervour is either motivated by selfish ego, worldly ambition or demonic temptation: often it is a mixture of all three.  But the Lord has the right to challenge us, searching our hearts and motives (Psalm 139:23-24).  That happens as we read His Word and allow Him to speak to us (Hebrews 4:12-13).  "Why?" is a great question because it unlocks motives.  Often, we do not know what provokes us to action until the Lord challenges us. But when He exposes our deceitful hearts, and we repent, it is the beginning of being truly useful to Him (2 Corinthians 7:8-9).