Isa 11:10-11 "And in that day there shall be a Root of Jesse, who shall stand as a banner to the people; for the Gentiles shall seek Him, and His resting place shall be glorious." It shall come to pass in that day that the Lord shall set His hand again the second time to recover the remnant of His people who are left...
The crucifixion of our Lord Jesus obsoleted the Old Covenant, thus sending all Jews to damnation. As prophesied, only a remnant would be saved. So at Pentecost out of God's grace, the Holy Spirit (New Spirit) was poured upon all the devout Jews for they spoke in tongues. 3,000 Jews accepted the Lord and were baptized. These were discipled and with the change of heart (new heart) they preached the gospel of grace to other Jews.
Eze 18:30-31 "Therefore I will judge you, O house of Israel, every one according to his ways," says the Lord God. "Repent, and turn from all your transgressions, so that iniquity will not be your ruin. Cast away from you all the transgressions which you have committed, and get yourselves a new heart and a new spirit. For why should you die, O house of Israel?
Acts 11:19-21, 25 Now those who were scattered after the persecution that arose over Stephen traveled as far as Phoenicia, Cyprus, and Antioch, preaching the word to no one but the Jews only. But some of them were men from Cyprus and Cyrene, who, when they had come to Antioch, spoke to the Hellenists, preaching the Lord Jesus. And the hand of the Lord was with them, and a great number believed and turned to the Lord...Then Barnabas departed for Tarsus to seek Saul.
After the death of Stephen, the disciples dispersed throughout the middle East and led many devout Jews to the Lord. Synagogues were filled with Christians and this was the fulfillment of Jewish remnant being saved in many countries. Gentiles (possibly outside) were allowed to listen to messages shared in synagogues. By then many Gentiles were already saved.
Acts 13:42-43 So when the Jews went out of the synagogue, the Gentiles begged that these words might be preached to them the next Sabbath. Now when the congregation had broken up, *many of the Jews and devout proselytes followed Paul and Barnabas*, who, speaking to them, persuaded them to continue in the grace of God.
Acts 13:44-46 On the next Sabbath almost the whole city came together to hear the word of God. But *when the Jews saw the multitudes, they were filled with envy; and contradicting and blaspheming, they opposed the things spoken by Paul*. Then Paul and Barnabas grew bold and said, "It was necessary that the word of God should be spoken to you first; but since you reject it, and judge yourselves unworthy of everlasting life, behold, we turn to the Gentiles."
By then almost all the devout Jews were already saved. The leftover unrighteous Jews opposed the gospel and persecuted Paul and Barnabas. So Paul and Barnabas turned to the Gentiles, who were hardly touched.
Acts 14:1 Now it happened in Iconium that they went together to the synagogue of the Jews, and so spoke that a great multitude both of the Jews and of the Greeks believed.
Since then Paul and Barnabas preached to both Jews and Gentiles in New fields where many were saved.
Acts 14:23 So when they had appointed elders in every church, and prayed with fasting, they commended them to the Lord in whom they had believed.
The intellect Paul with God's wisdom and knowledge was able to set up the church governance by appointing elders in each church.