Answer: The Gentiles are the other sheep of Christ. “Gentiles” are the non-Jews. In the Old Testament, the nation of Israel was the chosen people to be educated to bring out the Messiah. And when the Messiah comes, the whole world would be included to be rescued from sin. That includes all people outside the little nation of Israel in the coverage of Christ’s blood. So in the Great Commission, the disciples were commanded to go into all the world to preach the GOSPEL.
Exodus 19:5, 6, “Now therefore, if you will indeed obey My voice and keep My covenant, then you shall be a special treasure to Me above all people, for all the earth is Mine. And you shll be to Me a kingdom of priests and a holy nation.. These are the words which you shall speak to the children of Israel.”
Psalm 147:19, “He declares His word to Jacob, His statures and His judgments to Israel. He has not dealt with any nation; and as for His judgments, they have not known them.”
John 10:16, “I have other sheep that are not this fold; I must also ring them in, and they will hear my voice. There will be one flock, and one shepherd.”
At the early stage of Christ’s ministry, after He has called the twelve apostles and had trained them for a period of time, He sent them out in what is called the “Limited Commission” to the nation of Israel. This is recorded in Matthew 10: 1-42.
But later in His ministry our Lord revealed that there are other people who are included which He calls His other sheep. He Himself started in a limited way to touch these outsiders in the northwestern boundaries of two tribes: Zebulun and Neftali which are the areas of Lebanon and Sidon. See Matthew 4:13-17. This inclusion of the Gentiles was prophesied by Isaiah 9:2. Note that Isaiah 9:6 mentions the Messiah.
After Christ resurrected from the tomb, He met his disciples and gave them the Great Commission in Matthew 28:18-20 and Mark 16:15-16. The whole world is the field of harvest. Much later just before He ascended back to heaven, Christ told the disciples to be witnesses in Jerusalem, in Judea, in Samaria and to the uttermost part of the world.
By his birth, Greek education and young days, Saul (who became Apostle Paul), was born in Tarsus of Syria. He was providentially converted by Christ while he was chasing Christians who ran away from Jerusalem. Along the highway going to Damascus, he was knocked down with an intense light and was changed from persecutor into a disciple.
The Law which was given to the Jews at Mount Sinai that pronounced the Jews as a special people was taken out of the way at the cross. See Ephesians 2:11-22. Christ mediated a New Covenant confirmed by His death (Hebrews 9:16-22). Apostle Paul was especially assigned to the Gentiles. See Acts 9:15; Romans 1:16; Romans 9:1-5 and Gal. 2:9.
Romans 11 mentions the end of the special place of Israel as a chosen nation and ushering in of the Gentiles.