Revelation 19: 15: And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.
In the Millennium, the sinful nature of the unregenerate man will still exist. When Christ and His Bride are ruling over the nations, they are exercising dominion over a world of people who still have the old nature, but that nature is made subject to the absolute authority of Christ in a Kingdom where righteousness is established with a rod of iron. This rod of iron will also be wielded by Christ’s Bride (Revelation 2: 26 – 27), for She will be given power over the nations, and will be a strong, capable, unbending ruler who can cope so powerfully with any situation, that even the most desperate enemy will be broken if need be.
It is those who survive Armageddon that will repopulate the earth in the Millennium, and over which Christ and His Bride will rule. In a thousand years, the earth will have become filled with billions of people, and when Satan is loosed at the end of the Millennium, he will deceive and gather to himself all those people who do not have the Holy Ghost (the new birth) to make war against Christ, His Bride and the city of Jerusalem (Revelation 20: 7 – 9). These are people who have been reformed by the rule of Christ, but their hearts remained unchanged. They still have the power of choice (free moral agency), but because they are of wrong seed, they will eventually join with Satan and rebel against the Creator.
It is not until the restored earth that there is no more death (Revelation 21: 1 – 4), so in the Millennium, death is still present and the sinner will die an early death for refusing to submit to Christ’s rule and abide by the Law of His Word. Isaiah 65: 20 makes all this very plain: There shall be no more thence an infant of days, nor an old man that hath not filled his days: for the child shall die an hundred years old; but the sinner being an hundred years old shall be accursed. The longevity of man that existed before the Flood will return again in the Millennium, but for the sinner who is smitten with an early death because of disobedience, they will be considered but a child in comparison to those who live for hundreds of years.
The rod of iron is a reign of righteousness that is most rigorous and stern for the unbeliever, and which is heavily enforced. Zechariah 14: 16 – 19 gives an example of God’s justice upon those who refuse to keep His Law in the Kingdom Age: And it shall come to pass, that every one that is left of all the nations which came against Jerusalem shall even go up from year to year to worship the King, the LORD of hosts, and to keep the feast of tabernacles. And it shall be, that whoso will not come up of all the families of the earth unto Jerusalem to worship the King, the LORD of hosts, even upon them shall be no rain. And if the family of Egypt go not up, and come not, that have no rain; there shall be the plague, wherewith the LORD will smite the heathen that come not up to keep the feast of tabernacles. This shall be the punishment of Egypt, and the punishment of all nations that come not up to keep the feast of tabernacles. The Bible is very plain on these things and gives us a deep insight of the Kingdom Age; in fact, there is more scripture in the Bible about the Millennium than of any other period, and it is these finer details that are often not taken into account when people think about what the Millennial world will be like. We often imagine with thoughts of fantasy how things will be, but our thinking is generally far removed from what the scripture actually says. The earth will indeed be a wonderful place to live during the Millennium, but for the unregenerate, God’s Law is very stern and no tolerance will be made for any compromise.