You mention that there will be those who oppose Christ during His reign in the Kingdom. Who might oppose Him?
In the Millennial Kingdom, the world will be populated by two kinds of individuals: glorified human begins and natural (i.e., sinful) human beings.
The glorified human beings are those who were resurrected into new, sinless bodies prior to the start of the Kingdom, both Old Testament and New Testament saints. The natural human beings will be men and women descended from Adam (like us) and born during the Kingdom age. So like us today, these people will occupy sinful bodies that naturally oppose God. The glorified population will reign over the natural population, which must be ruled because of their sinful nature.
These sinful men and women will be the descendants of believers who enter the Kingdom coming out of Tribulation (i.e., the “sheep” separated from the “goats” in Matthew 24). Since these believers never died prior to the start of the Kingdom, they were never resurrected into glorified bodies. Therefore, they enter into the Kingdom in the nature of Adam and are able to reproduce as we do today. Their descendants give rise to an unbelieving population in the Kingdom. (You can learn about these two populations in detail by listening to our Revelation Bible study on our website.)
In Revelation 20 we’re told that at the end of the age, the enemy will be released so he can deceive the nations of natural descendants living in the Kingdom to rebel against Christ’s rule:
Notice that the natural (i.e., unsaved) population of the Kingdom will grow over the thousand years to reach the point of an uncountable number. They will come against Christ, yet He will prevail and bring Satan and his forces. For a complete understanding of the Kingdom, please listen to our Revelation Bible study, particularly lessons 20A-20D.