Act 11:1-3 Now the apostles and brethren who were in Judea heard that the Gentiles had also received the word of God. And when Peter came up to Jerusalem, those of the circumcision contended with him, saying, "You went in to uncircumcised men and ate with them!"
Just before our Lord Jesus went back to heaven, He commissioned all His disciples to made disciples of all nations including Gentiles. But when Peter reached the Gentiles, these disciples forgot the commission of our Lord and instead confronted Peter for the salvation of Gentiles.
Gentiles' Salvation by God's grace
Act 11:15-17 And as I began to speak, the Holy Spirit fell upon them, as upon us at the beginning. Then I remembered the word of the Lord, how He said, 'John indeed baptized with water, but you shall be baptized with the Holy Spirit.' If therefore God gave them the same gift as He gave us when we believed on the Lord Jesus Christ, who was I that I could withstand God?"
The distinct physical evidence a Christian is the manifestation of the gift of tongue of all the gifts of the Holy Spirit. So God used the gift of tongue to confirm their salvation. The moment the rest of the Apostles and elders in Jerusalem heard that the Gentiles were given the gift of tongue, they were convinced.
Act 11:18 When they heard these things they became silent; and they glorified God, saying, "Then God has also granted to the Gentiles repentance to life."
Reluctant to reach Gentiles
Acts 11:19-21 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.
Though the disciples led many Hellenists (Greek speaking Jews) to the Lord, yet they will not touch the Gentiles who were also Greek speaking. When Barnabas saw the multitudes of new converts, he went to get Paul's help to disciple them.
Act 11:25-26 Then Barnabas departed for Tarsus to seek Saul. And when he had found him, he brought him to Antioch. So it was that for a whole year they assembled with the church and taught a great many people. And the disciples were first called Christians in Antioch.
Persecutions by King Herod
Acts 12:1-3 Now about that time Herod the king stretched out his hand to harass some from the church. Then he killed James the brother of John with the sword. And because he saw that it pleased the Jews, he proceeded further to seize Peter also. Now it was during the Days of Unleavened Bread.
The martyrdom of Stephen by the Jewish leadership did not scatter the Apostles, who preferred the comfort and respect in Jerusalem. Their job then was mainly to disciple the few converts in Jerusalem and also to evangelise devout Jews coming back to Jerusalem to worship in the temple of God during the feasts.
Note - God left the temple of God at the death of Jesus on the cross and since then every physical body of born again Christians is the temple of God.
Revival were everywhere - in Judea, Samaria and neighbouring countries and yet these Apostles were still staying put in Jerusalem.
The martyrdom of Apostle James and the persecutions of Apostles and church leaders in Jerusalem scattered them so that they could disciple the multitudes of new converts.