It may surprise some today to learn that the Jews exercised an impressive missionary effort among the gentiles of the first century CE. Hillel is considered to be one of the most beloved Pharisees of ancient Judaism, and he advocated that the Jews would “love your fellow-creatures, and draw them near to the Torah” [Babylonian Talmud: Seder – Nezikin: Avoth, chapter 1, Mishna 12]. Jesus himself accused the Pharisees of proselytizing the world to find one single disciple and then made him twice the son of hell as themselves (Matthew 23:15).
If we consider such a man as Saul, who was very zealous for the traditions of his fathers (Galatians 1:14), we should consider the possibility that he went out from Jerusalem seeking to make proselytes of gentiles, before he actually met Jesus on the Damascus road. Speaking of Jewish missionaries [called Judaizers in some commentaries] Paul tells new believers in Christ that they zealously court the attention of others, but not sincerely. What they do is isolate their prospects from those they know, from their comfortable surroundings, friends and family etc. in order that the prospective proselytes would zealously court the attention of the Jewish missionaries (cp. Galatians 4:17). That Paul was at one time a Jewish missionary to gentiles before his conversion gains some support in Galatians 5:11. There those who sought to corrupt the faith of the new believers in Galatia accused Paul of preaching circumcision, just as they were doing. However, Paul’s logic is – if he was still preaching circumcision (implying he did at one time), why is he being persecuted for preaching the Gospel?
Josephus records for us that Jewish missionaries successfully converted the ruling family of Adiabene in Mesopotamia cir. 47 CE [Josephus: Antiquities 20.2.1]. Luke in Acts 2 lists proselytes from Rome among those to whom Peter preached on Pentecost 31 CE. One of the leading Messianic believers was Nicolaus the proselyte of Antioch (Acts 6:4). Philip, one of the Seven (Acts 6), was told in a vision to preach Jesus to an Ethiopian eunuch who was a Jewish proselyte returning to Ethiopia after worshiping at Jerusalem (Acts 8:26-39). Moreover, Peter himself was sent to a God-fearer named Cornelius, a Roman centurion living in Caesarea, and Paul seems to have preached to another God-fearer named Sergius Paulus in Cyprus, and sent by him to his home town in Pisidian Antioch to preach to his family of God-fearers in the local synagogue there. So, evidence seems to point to a considerable amount of Jewish evangelistic effort spent among the gentiles in the 1st century CE, showing that the Jews of that day were especially zealous to bring gentiles into obedience to the Torah (Isaiah 43:10-12, 21).
It was into this scenario that Barnabas and Paul came into Galatia, and Pisidian Antioch in particular. The harvest field of the Gospel began in the synagogue, for the Gospel must go to the Jews first (Acts 13:46; cp. Romans 1:16). It was here that Paul found a ripe field to form a strong nucleus for the churches he would raise up. Here he found Jews and gentile proselytes and God-fearers willing to embrace the Gospel of the Kingdom.
It also must be remembered that Paul was not ‘stealing’ from the Jews or taking for himself or for Christianity what zealous Jews worked hard to achieve. At this point in time, there was nothing in the world that could legitimately be called Christianity. Although gentile unbelievers called us Christian, we called ourselves Followers of the Way. We didn’t begin calling ourselves Christian until the 2nd century CE. What Paul was doing was a legitimate Jewish labor. The Messianic movement or The Followers of the Way was considered an authentic Jewish sect along with the Pharisees, Sadducees and Essenes—to name a few. If what Barnabas and Paul were doing was **not** considered a legitimate Jewish undertaking, why did the high priest at Jerusalem believe he had authority over what Paul was doing? It wouldn’t be legal for Jewish authorities at Jerusalem to punish a Roman citizen (as Paul was) for crimes not of a Jewish nature.