In most of our Bibles, the heading inserted over Acts 9 reads, "Saul's conversion", or something similar. The common thought is that when Saul had his encounter with the risen Jesus on the road to Damascus, he left his former religion, Judaism, and embraced a new religion, Christianity. Even his name was changed to reflect the dramatic change in his outlook.
This all makes for great drama, but besides the anachronism of considering Christianity to be a separate religion in the mid-first-century, there are abundant reasons in the text to question this interpretation of events.
First of all, in all the passages which comment on this event, in Acts 9, 22, 26, and Galatians 1, there is nothing that can be interpreted as a conversion from one religion to another. The emphasis is on a calling to a particular ministry, that of taking the gospel to the Gentiles.
Krister Stendahl, in his book Paul Among Jews and Gentiles, points out that the language Paul uses in his own accounts of this event are similar to the calling of the prophets Isaiah, Jeremiah, and Ezekiel. (Isaiah 49:1; Jeremiah 1:5; Ezekiel 2:1-3) God had set him apart from before birth and was now delivering the commission to preach a particular message to a particular audience.
It is instructive too that the man through whom this commission is mediated, Ananias, is described in Acts 22:12 as "a devout observer of the law and highly respected by all the Jews living there". It is apparent that Saul's experience on the Damascus road did not result in his abandoning Torah or the Jewish faith. This is especially evident when we observe how he identifies himself religiously after this experience.
Saul or Paul?
Paul's Religious Self-Identification