A.T. Robertson Commentary Acts 9:5

"And he said, Who art thou, Lord? And he [said], I am Jesus whom thou persecutest:" — Acts 9:5 (ASV)

Lord (κυριε). It is open to question if κυριε should not here be translated "Sir" as in 16:30 and in Mt 21:29,30; John 5:7; 12:21; 20:15; and should be so in Joh 9:36. It is hardly likely that at this stage Saul recognized Jesus as Lord, though he does so greet him in 22:10 "What shall I do, Lord?" Saul may have recognized the vision as from God as Cornelius says "Lord" in 10:4. Saul surrendered instantly as Thomas did (John 20:28) and as little Samuel (1 Samuel 3:9). This surrender of the will to Christ was the conversion of Saul. He saw a real Person, the Risen Christ, to whom he surrendered his life. On this point he never wavered for a moment to the end.