Dr. Mark Hitchcock likes to call the 1000 years as the front porch of eternity. It's like Phase 1 of God's eternal kingdom.
After Christ has ruled and reign for 1000 years, and fulfilled all of God's promises for this earth, God is going to destroy this present heaven and earth. He is going to make a new heaven and a new earth.
God spoke it into existence and He is going to speak it out of existence.
In the New Jerusalem, there are 12 gates inscribed with the names of the 12 tribes of Israel.
If you think back into the 12 Patriarchs of Israel, they sold their brother into slavery and they let their father think that he is died. Yet, the 12 gates that lead into the new Jerusalem have their names on it.
It speaks loud and clear that no matter what one have done in their lives, you can be redeemed through Jesus Christ.