Why did Saul ask 'Who art thou, Lord?' when Jesus spoke to him?
Saul asked because he immediately recognized the heavenly voice as God, specifically Jehovah, the God of Abraham. Since he understood he was dealing with Jehovah, he asked who was speaking. The answer identified the speaker as Jesus, the same Jehovah who had called Abraham and spoken to Moses and David.
Les explains that when Saul responded, 'Who art thou, Lord?' he immediately knew he was dealing with God, and that is why he asked the question. In the original it really should be Jehovah, because Jehovah was the God of Abraham, so Saul's question was essentially, 'Who are you?' The answer was, 'Well I'm Jesus.' Les asks us to imagine the man's reaction: the one Saul thought was such an imposter and blasphemer, and whose name he was trying to obliterate from Jewish thinking, was the same Jehovah who had called Abraham, spoken to Moses, and spoken to David. This was the same one now speaking from heaven after having been crucified, buried, and risen from the dead. That voice from heaven said, 'I am Jesus whom you persecuted.'
And he said, Who art thou, Lord? And the Lord said, I am Jesus whom thou persecutest: it is hard for thee to kick against the pricks.
More Questions
Why does Les say Saul's 'Who art thou, Lord?' should really read 'Jehovah'?
In the original text Saul's word 'Lord' should really be 'Jehovah,' because Jehovah was the God Saul understood, the God of Abraham.
When Saul asked 'Who art thou, Lord?' on the Damascus road, who answered him?
When Saul of Tarsus encountered the light and voice on the Damascus road, his question "Who art thou, Lord?" was in effect asking "Who art thou, Jehovah?" — and Jehovah answered him, "I am Jesus."
Why did Saul ask 'Who art thou, Lord?' after seeing the light from heaven?
When Saul saw the penetrating light coming from above, his instinct (second nature) told him that his God—the God of Abraham, Isaac, and Jacob—was dealing with him, and so he asked, 'Who art thou, Lord?'
Why did Saul ask 'Who art thou, Lord?' instead of 'Who art thou, Jehovah?'
Saul would have said 'Who art thou, Jehovah?' if he had not had such an awe for the divine name in all practical circumstances; his reverence for the name made him address the voice as 'Lord.'