Acts 22:8

“And I answered, ‘Who are you, Lord?' And he said to me, ‘I am Jesus of Nazareth, whom you are persecuting'.”

But he had not been able to see how what he was doing was persecuting God, so he had asked, ‘Who are you, Lord?' And the reply had been that it was Jesus of Nazareth Whom he was persecuting. To persecute His followers was to persecute Him. Whatever else this proved it demonstrated that Jesus was alive and in heaven and approved of by God, for here He spoke from God. It was proclaiming the living, resurrected and enthroned Lord.

It was also a strong hint to the crowd. They too were persecuting Jesus when they should instead be listening to Him and acknowledging His resurrection. It had not been a secret. They too should be saying, ‘Who are you, Lord?'