Here is a nettle which we must grasp if we are to understand the relevant issues that swirl around apocalyptic speculations, not least those surrounding the Millennium.* When people hear talk about "heaven" and "earth", in our culture they normally assume that these terms refer to places at a great distance from each other. Many people still think that "heaven" is "way beyond the blue", a place up there in, or above, the sky. Even though most people know it isn't like that, the picture is naggingly resistant to serious thought.
Talk of "heaven" and "earth", though, comes to us mostly from the Bible; and in the Bible these are not two places, separated from each other by many miles, but two different dimensions of the total reality of the world. This is what I mean by a "duality", as opposed to a "dualism". Just as animals, and many plants, are irreducibly male and female, with the two being complementary, and both being good and necessary for the flourishing of the species, so "heaven" and "earth" are the two dimensions of created reality. These two God-given dimensions interlock and interact in a variety of ways, sometimes confusingly, often surprisingly. And it's particularly important to notice that heaven and earth were both created good. It isn't the case that the physical world is somehow shabby or second-rate, and the non-physical somehow morally superior. That is to move into dualism, setting the two worlds against each other. Indeed, in the biblical story evil infected both spheres: creatures in heaven as well as creatures on earth, we are told, rebelled against God. But in that same story all things, in both spheres, are reconciled thorugh Jesus the Messiah, though only after the principalities and powers, the spiritual powers that attempted to usurp God's place, had been defeated through Jesus' crucifixion (Colossians 1.15-20; 2.14-15).
My point is this: the duality between heaven and earth is very different from the dualisms of sectarian religion. The midset that tends towards apocalypticism normally thinks of the heavenly realm, or the spiritual realm, or simply the non-physical realm, as always good, and the earthly, material, physical world as always bad. Hence the readiness to imagine the present physical world being blown apart in some great Armageddon, and the sublime confidence that "we"--whichever group that might be--will be rescued from the ruin in a "heavenly" salvation that has left earth far behind.
--N.T. Wright, The Millennium Myth, Westminster/John Knox 1999, pp. 37-38
*"Millennium" here refers to the advent of the year 2000, which is the basic theme of the book.