The millennium will not just consist of Gentiles and not just Jews- Mt.25 speaks of sheep that will enter the millennium who helped the brethren. The goats are unbelievers that are judged. This means everyone that will enter the 1,000 year reign of Christ on earth will be saved. But not all will be glorified having resurrected bodies. Only those who come back with Christ will have sinless bodies to co rule and reign under him as King. They will have tom wait until the thousand years are up to receive the transformation.

 The sheep in Mat. 25:33 enter the kingdom prepared for them before the foundation of the world. Where is this kingdom? the kingdom is where Christ is ruling which will be in Israel, Jerusalem (Mt. Zion) as he rules the nations with a rod of Iron. The people of the nations are first those who are saved. Satan will be bound so the only sin will come from mans fallen nature.

  In the millennium the world will be built back up. People will be born to the saved who enter the Millennium and as this increases so will those who do not believe even though Christ will be ruling and only his teaching will be upon the earth Hab 2:14: “ For the earth will be filled with the knowledge of the glory of the LORD, as the waters cover the sea.”

Isa 65:19-25 I will rejoice in Jerusalem, and joy in My people; the voice of weeping shall no longer be heard in her, nor the voice of crying. "No more shall an infant from there live but a few days, nor an old man who has not fulfilled his days; for the child shall die one hundred years old, but the sinner being one hundred years old shall be accursed. They shall build houses and inhabit them; they shall plant vineyards and eat their fruit. They shall not build and another inhabit; they shall not plant and another eat; for as the days of a tree, so shall be the days of My people, and My elect shall long enjoy the work of their hands. They shall not labor in vain, nor bring forth children for trouble; for they shall be the descendants of the blessed of the LORD, and their offspring with them. "It shall come to pass that before they call, I will answer; and while they are still speaking, I will hear. The wolf and the lamb shall feed together, the lion shall eat straw like the ox, and dust shall be the serpent's food. They shall not hurt nor destroy in all My holy mountain," says the LORD.”

At the completion of the 1,000 years the people will be tested just as Israel was tested in the wilderness(Heb.3:8-9) and the tribulation. They will be tested on whom they will choose to have allegiance to.

Zech. 13:8-9 And it shall come to pass in all the land," says the LORD, "That two-thirds in it shall be cut off and die, but one third shall be left in it: I will bring the one-third through the fire, will refine them as silver is refined, and test them as gold is tested. They will call on My name, and I will answer them. I will say, 'This is My people'; and each one will say, 'The LORD is my God.'"

Rev 20:7-8 “Now when the thousand years have expired, Satan will be released from his prison and will go out to deceive the nations which are in the four corners of the earth, Gog and Magog, to gather them together to battle, whose number is as the sand of the sea.”After the 1,000 years Satan is released to test the people who he had no influence on . (for the first time in history he was unable to influence generations). These are people that will be influenced for the final rebellion against Jesus

Rev 20:9-10 “They went up on the breadth of the earth and surrounded the camp of the saints and the beloved city. And fire came down from God out of heaven and devoured them. The devil, who deceived them, was cast into the lake of fire and brimstone where the beast and the false prophet are. And they will be tormented day and night forever and ever.”

Then the culmination of the ages where everything is transformed to be in a state without sin.

Rev 21:1-5 “Now I saw a new heaven and a new earth, for the first heaven and the first earth had passed away. Also there was no more sea. Then I, John, saw the holy city, New Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband. And I heard a loud voice from heaven saying, “Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people. God Himself will be with them and be their God. “And God will wipe away every tear from their eyes; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away.” Then He who sat on the throne said, “Behold, I make all things new.” And He said to me, "Write, for these words are true and faithful."