This question mainly deals with Revelation 21:24–27, but it is probably helpful to read from Rev 20 to the end also.
Revelation 21 (KJV)
24 And the nations of them which are saved shall walk in the light of it: and the kings of the earth do bring their glory and honour into it. 25 And the gates of it shall not be shut at all by day: for there shall be no night there. 26 And they shall bring the glory and honour of the nations into it. 27 And there shall in no wise enter into it any thing that defileth, neither whatsoever worketh abomination, or maketh a lie: but they which are written in the Lamb's book of life.
I understand that these nations of the new earth are not procreating, however, there are supposedly people who are evil that are being kept out of the holy city at this time. Where are they coming from if no one is having babies?
You would think, that at this time all the people that are found in the Lamb's book of Life have eternal bodies, and the others are in the lake of fire. Somehow these evil people in question should be in the lake of fire instead of being kept out of the gates of the holy city of the new earth, one would think. The mere problem that sin is still with us in the new earth seems, well, weird.
A good answer will be from the premillennial perspective, pre- or post-tribulation shouldn't matter.