A crucial matter is solved by the Parable of the Sheep & Goats: how the rebels of the Millennial Kingdom are produced.
The Sheep are separated by the King from the Goats. Where do the Sheep go? They are destined to join in their human bodily state the glorious reign of Christ on Earth during His Millennial reign. The resurrected believers arrive with Christ in their spiritual bodies, and they do not reproduce physically.
Only the Sheep believers have bodies and they reproduce during the years of this Millennial Reign. Some of their progeny/children will rebel against the King.
This is how the crucial issue of the rebels during the Millennial is resolved. The Sheep provide the solution to this matter.