Acts 9:5

And he said, Who art thou, Lord? and he said, I am Jesus whom thou persecutest.

Who art thou, Lord? ... This is the great question which must engage the mind of every person who would be saved. Angels bend low over the head of any man who earnestly seeks the answer; for it is who Jesus is and was and ever is that endows his holy religion with relevance and authority for all who ever lived.

As Howson declared:

This revelation was not merely an inward impression made on the mind of Paul during a trance or ecstasy; but it was the direct perception of the visible presence of Christ.[13]

Paul asked, "Have I not seen Christ?" (1 Corinthians 9:1); and upon mentioning the appearances to the Twelve, he said, "He was seen last of all by me" (1 Corinthians 15:8). Ananias stated that our Lord "appeared to (Paul) in the way" (Acts 9:17). Thus the New Testament affirms that this was a genuine appearance of Jesus of Nazareth to Saul of Tarsus.

As Bruce said:

The more one studies the event, the more one agrees with the eighteenth-century statesman George Lyttleton, that "the conversion and apostleship of Paul alone, duly considered, was of itself a demonstration sufficient to prove Christianity to be a divine revelation."[14]

[13] J. S. Howson, op. cit., p. 75.

[14] F. F. Bruce, op. cit., p. 196.