
The New Perspective on Paul calls this traditional view into question. James Dunn has built on the work of Krister Stendhal to argue that Paul did not experience a conversion from one religion to another. Rather, Paul received a call of God that is quite parallel with the prophetic calls of the Hebrew Bible, especially that of Jeremiah. The Damascus Road experience as a theophany, not unlike what Isaiah experienced in Isaiah 6. Paul experienced the glory of God and was called to a prophetic ministry. Paul never left Judaism, Stendahl argued, he remained a faithful Jew who was fulfilling the role of being the “light to the Gentiles” from Isaiah. (Not all scholars who are associated with the New Perspective agree, N. T. Wright still talks about “Paul’s Conversion” in What Saint Paul Really Said.)
Dunn points out that Paul stayed “zealous,” but instead of zealous for the Law, he because zealous as the “light to the Gentiles” (“Paul’s Conversion,” 90). This view of Paul’s conversion is that he does not “found a new religion” but rather a new understanding of the Jewish Law. His gospel is a new interpretation of the Hebrew Bible and Judaism. Paul may not changed have even parties within Judaism: he went from a Pharisee who did not believe Jesus was the messiah to a Pharisee who did believe Jesus was the messiah.
The problem with this new view of Paul’s experience on the road to Damascus is that it does not do justice to the radicalness of Paul’s Gospel! To reject circumcision even for Gentile converts is not a minor re-interpretation of the Jewish Law, it is a radical change that is unanticipated in the prophets. The reaction of the Jews in Acts is key. Everywhere Paul announces that God has called the Gentiles to be saved without circumcision, they riot and attempt to kill Paul.
Philippians 3:7-8 make it clear that Paul is not just moving to another party within Judaism, but rather that he is rejecting his Pharisaic roots completely. He is breaking with his past way of life and his past theology. While there are many points of comparison between Paul’s theology and Judaism, there are significant radical breaks with the Judaism of the first century. While it is possible Paul thought he was staying within Judaism, his contemporaries disagreed. (I suspect that includes not a few Christians Jews who disagreed with his view of the Law for Gentiles.)
But it is also problematic to think that Paul is converting from Judaism to Christianity. Paul seems rather clear in Galatians that he was called by God to be the apostle to the Gentiles in a way that is quite distinct from the apostles in Jerusalem that were called by Jesus. He stresses his independence clearly in Galatians, in Ephesians 3 he is quite clear that he has a special commission as the apostle to the Gentiles.

It is probably best to see Paul’s Damascus Road experience as both a conversion and a call. I agree that Luther and others hear their own conversion in Paul’s Damascus Road experience. But to think of the categories “conversion” and “call” in modern Christian categories is a mistake, Paul’s experience in Acts 9 is quite unique in salvation history.
Bibliography: There is a huge bibliography of essays and monographs on this issue; the critical articles include: J. D. G. Dunn, “‘A Light To the Gentiles’ or ‘The End of the Law’? The Significance of the Damascus Road Christophany for Paul” in Dunn, Paul, Jesus, and the Law, 89-107. See also Seyoon Kim, The Origin of Paul’s Gospel (Grand Rapids, Mich.: Eerdmans, 1982); After Kim was critiqued by J. D. G. Dunn and others, he responded in a number of articles that are collected in Paul and the New Perspective: Second Thoughts on the Origin of Paul’s Gospel (Grand Rapids, Mich.: Eerdmans, 2002).