How does the earth's population at the end of the Millennium compare to today's population?
By the end of the Millennium, the earth's population will probably be as large as or larger than today's population. The millennial Kingdom will see a tremendous population explosion, so that when Satan is released to test them, there will be as many people or more than there are right now.
Les explains that during the Tribulation, God is still preparing Gentiles to enter the Kingdom in ordinary flesh and blood bodies. Because the Kingdom experiences a tremendous population explosion, by the end of the thousand years, when Satan is released to test them once again, there will probably be as many people on the earth or more than there are right now. This contrasts with the cataclysmic judgments described in Isaiah 24, which will empty and waste the earth during the final seven years before the Kingdom.