Acts 22:6
And it came to pass, that, as I made my journey, and was come nigh unto Damascus about noon, suddenly there shone from heaven a great light round about me. And it came to pass, that, as I made my journey, and was come nigh unto Damascus about noon, suddenly there shone from heaven a great light round about me.
As he made his journey and was come nigh unto Damascus about noon, while traveling there to persecute the followers of Jesus whom he had previously opposed, suddenly there shone from heaven a great light round about him. That light surrounded his companions as well, was brighter than the sun and too glorious for mortal eyes, and brought Saul to the ground. The encounter was his conversion, when his proud heart bowed to serve Christ.
In the light Jesus revealed himself as the crucified Nazarene, the crucified and risen Messiah, exposing Saul's error, and taught him that he was the Son of God. Christ's words in the encounter identified persecution of his people as persecution of Christ himself. Paul told this event to the Jerusalem crowd to explain how he changed from a persecutor to a servant of Christ. His conversion together with the later vision in the temple directing him to the Gentiles shows his mission was given by God and not chosen from preference.