Luke treats Paul’s Damascus road experience as a very important event in his thesis, mentioning it three times. First, he describes the event as part of an historical narrative concerning the spreading of the Kingdom of God (Acts 9). However, later he has Paul recall the event, describing what occurred in his own words to the Jews at Jerusalem, including the Jewish authorities (Acts 22). Finally, Luke has Paul recall the event before King Agrippa, while other important authorities listened, including the Roman governor, Festus (Acts 26).
Most conversions to Christianity, today, occur when someone admits that his present religious beliefs are wrong or unsatisfactory or when someone without any religious background whatsoever (an atheist or agnostic) concludes he is wrong and embraces Jesus as his Savior and Lord. In other words it is a clear and complete change in one’s life, from believing and acting one way to becoming a follower of Jesus; and this change or conversion experience is noticeable to everyone that the new believer knows.
The problem is: what did Saul change from or leave behind in order to embrace Christ? What did Saul believe in Jerusalem that was set aside in Damascus in order to receive Jesus as Lord and Messiah? Later, when Paul was making his defense before Felix concerning his life’s work and his most recent activity in Jerusalem, he claimed the he worshiped the God of his fathers, believing all the things written in the Law and the Prophets, and when he was arrested and accused of evil-doing, he was found in the Temple practicing the Jewish traditions of purification (Acts 23:14-21). In other words, Paul’s defense before Felix and the high priest who had come down to Caesarea to accuse him was that he was a Jew, practicing his religious beliefs as all good Jews do!
So, from what was Saul converted? Before embracing Jesus as Savior, he was a Jew by faith, and, after his experience on the road to Damascus, he was a Jew by faith! Clearly, Paul viewed his religious activity as a believer in Jesus in a very Jewish way, just as many Jews viewed their religious activity but did not embrace Jesus as their Messiah. It does not appear that Saul/Paul distinguished what we, today, call Christianity from what he confessed as the Jewish faith.
Furthermore, Messianic Judaism existed in unity with Pauline “Christianity” throughout the era of the New Testament. Not only so, but throughout Paul’s ministry the same existed, as a sect of Palestinian Judaism, which did not embrace Jesus as Messiah. In fact, it is precisely because it was viewed as such that the Jewish authorities in Jerusalem assumed authority over what Paul was doing and desired to kill him. If Saul/Paul was a renegade, completely divorced from or excommunicated from the religion of his youth, the Jewish authorities in Jerusalem could have no authority over what he was doing. After all, what had they to do with Diana of Ephesus or Nero and the Emperor cult? If Paul wasn’t preaching traditional Judaism with Jesus as the promised Messiah, the Jewish authorities could not call him into question over his Gospel. So, I repeat: from what was Saul converted?
There are two words used in the New Testament that are translated into our English word convert or converted. They are epistrepho (G1994) meaning: to turn to or toward, or to return. It is derived from strepho (G4762), the second Greek word. Strepho means: to turn about or away from, to alter or adopt another course. Usually, both words are used in the New Testament for the turning of one’s body toward someone else. In Matthew 18:3 Jesus uses strepho to describe one becoming as a child, indicating a change of heart. In Acts 7:39 Stephen uses the same word to describe the fathers turning their hearts toward Egypt, and in verse-42 he uses it to describe God turning from them and giving the Israelites up to worshiping the heavens. In Matthew 13:15 and Mark 4:12 Jesus uses epistrepho to describe the condition of the hearts of the Jews who listened to him—they were willingly blind and refused to change or be converted (cp. Acts 28:27). In Luke 22:32 it appears that Peter was on a wrong course, but Jesus prayed for him and when he was converted or altered that course, he was to strengthen his brethren. Finally, James uses this same word in Acts 15:19 for gentiles who had turned to God.
It seems to me that Saul was converted from the course he was on, namely, persecuting the Jewish believers in Jesus, but he was not ever converted from the Jewish faith. For Paul Christianity, as the faith was later called, was the same faith as that of his ancestors. In fact, Christianity was the fulfillment of that faith—the promises made to the fathers were fulfilled in Jesus. To believe that Saul converted from Judaism to Christianity on the Damascus road would be a great error that would leave Paul’s ensuing faith and Gospel without any foundation or explanation. Rather, it is Paul’s Gospel that both gentiles and Jews are made one in Christ that most Jews of the 1st century found utterly abhorrent. Paul didn’t abandon the Jewish faith; rather, he received the gentiles into that faith through Christ.
On the other hand, what about Paul’s call? Paul had believed that he was commissioned by God—called—to be an Apostle to the gentiles (Romans 1:1; 1Corinthians 1:1; 2Corinthians 1:1; Galatians 1:1). Saul was, in fact, called by God to be an Apostle of Jesus while he traveled on the road to Damascus. It was this call that made his conversion a possibility. Before Saul saw and listened to Jesus, he was breathing out threats and slaughter against the disciples of the one God had cursed (Deuteronomy 21:23). In his vision of Jesus, Saul was able to see God’s vindication upon the One men had cursed (cp. Isaiah 53:4). In other words knowing Jesus had been resurrected by God showed Saul he was wrong, and seeing he was in error, he was able to repent and be converted. So, it was Jesus’ calling out to him that enabled Saul’s change of heart.