It had been Peter's duty and privilege to preach the Gospel first to the Gentiles. Please note that when the Lord desired the Gentiles to hear His word, He instructed the Chief of the Twelve to turn the key that opened the Gospel door to them. This is one of the special duties of the Apostleship.
Christians.
Since that time, many Gentiles had become converted; and in some cities they met and worshiped together with the Jews. This was particularly true in Antioch, an important city of Syria where the followers of Jesus were first called Christians.
But there were certain men from Judea who went to Antioch and caused trouble. These were Jews who had accepted the Gospel, but who still believed that the Gentiles would have to do everything the Jews did before they could obtain salvation.
Peter Justifies the Gentiles.
The question as to whether the Gentiles might receive the Gospel and be saved, without conforming to every Jewish rite, came before the Twelve and other Church leaders in Jerusalem.
"And when there had been much disputing, Peter arose up, and said unto them:
"Men and brethren, ye know how that a good while ago God made choice among us, that the Gentiles by my mouth should hear the work of the Gospel and believe.
"And God, who knoweth the hearts, bare them witness, giving them the Holy Ghost, even as he did unto us;
"And put no difference between us and them, purifying their hearts by faith."