One of the things that is overlooked, or even ignored, in the ministry of Paul is that when he was sent to the Gentiles, it is within the boundaries of the Torah-based faith of Israel. He was not bringing a “new faith” but was working within the only faith God ever gave mankind. This is an important point.
Many teachers portray Paul, Cornelius of Acts 10 and others as being “converts” to Christianity, but Christianity did not exist at the time, nor were the congregations in the New Testament “Christian” churches because there was no such thing in the first century. These things would not have been allowed under Roman law. From the time of Julius Caesar, Judaism was designated as “religio licita” and allowed to continue practicing their faith because they pre-existed Rome (see Josephus Antiquities of the Jews xiv 10.1-8). That’s why you see the Temple and the synagogue system flourishing in the Gospels and Epistles.
However, about the time of Nero, certain Gentile groups began separating themselves from the faith of Israel, believing that they “replaced” Israel in God’s plan, thus placing themselves outside of the religious parameters that Rome had set concerning the faith of Israel, or Judaism. As a result, a persecution was initiated by the Roman authorities against these entities because they were no longer under the protection of the allowed “pieties” in Judaism.
So, the real reason “Christians” were persecuted in the first century was not so much because of their faith in Messiah (Messianic synagogues who believed in Yeshua as Messiah were already established throughout the empire and allowed to exist) but for their rejection of the “faith of Israel” that the Lord had already established, ignoring Paul’s warning in the Book of Romans.
Paul made it very clear that his ministry was within the parameters that were allowed by Rome and it was a Torah-based faith (that’s why these synagogues existed in Rome itself). He wanted to provoke his countrymen to jealousy when they saw his ministry to the Gentiles, fulfilling what had been promised to the fathers and the prophets, thus proving that Yeshua was the promised Messiah. There would be no reason for the Jewish people to be jealous of another faith or religion outside of the faith that God had already given. Well-meaning people today try to “convert” Jews to Christianity believing that Christianity is now the faith that God has established, but that would mean that the Jews are no longer the “chosen” people and that they needed to “do way with” the faith that the Lord had given in the Scriptures and convert to a new religion (which tells them to do just that) in order to have a place in the Kingdom of God.
The Gospels and Epistles teach the exact opposite. It is the Gentiles who are grafted into the faith of Israel, which includes the Messiah (Rom 9.1-5), and Paul makes that point clear in Rom 11.11-24 and Eph 2.11-22. If the Jewish people had to convert to Christianity, then the eschatological view of the Scriptures concerning the Gentiles would not be fulfilled and this would certainly not achieve what Paul was trying to do among his Jewish brethren. And we have mentioned before, proposing a “new religion” outside of the faith of Israel would not only have been unbiblical, but illegal.
The turning of Gentiles from paganism to the faith of Israel is what the prophets have said for centuries (Zech 8.23; Isa 2.2-4; Jer 3.17; Zech 14.16-21; Isa 66.23-24; Mic 4.1-5 to name a few). Paul considered his ministry to the Gentiles to be on behalf of Israel and a fulfillment of prophecy. To try and bring Gentiles into a “new religion” would not have had the result Paul wanted and it would not have attracted the Jewish people at all because they would have considered it outside of what the Lord had had said in the Scriptures.
In our study of Replacement Theology on this site, we get into much more detail on this but Jews will never come to a new religion, or any religion, outside of the faith already given to Israel. However, during the Tribulation (the Birthpains), many Jews will come to a Torah-based faith in Yeshua through the ministry of the 144,000 Jewish men sent to them, and the ministry of the Two Witnesses, and they are described as having a testimony of Yeshua as Messiah and they keep the commandments of God (Rev 12.17).