Both heaven and earth were created by God and He said "it is good." Both eternity and time were created by God and that also was, and is, a good thing. In Adam’s fall, sin came into the world, but it was sin, and not creation, that was bad. Creation is cursed because of sin, but creation is not inherently sinful. This is an either/or problem. We tend to think it is either heaven or earth. I do think we need to prioritize eternity over time and heaven over earth but I do not think we have to (or even should) choose either one or the other. Fallen man tends to always go to one extreme (so heavenly minded, no earthly good) or the other (so earthly minded, no heavenly good).
The problem we have in Christianity today is that so much Gnostic or platonic thinking has permeated the Church. Plato taught that the body and all things physical were a distraction and a disadvantage to reason and the other so-called "real" world of forms and essences. Death, according to him, was not an enemy (as the apostle Paul taught 1 Cor 15:26) but a friend that released you from your prison of flesh and earthliness. If the material world is inherently bad there is no reason for Christians to redeem it. This is why monasticism and a dangerous form of pietism entered the church. Many retreated and withdrew from this present physical world. They were not seeking to claim the material world for Christ the King. They were escapists rather than stewards of God’s world.
We see this today in Dispensationalism and the "Left Behind" phenomenon. Christians are supposed to rebuild, not retreat. We are redeemed for dominion, not desertion. One of the reasons or results of the first coming (incarnation) of Jesus was "that we should be saved from our enemies and from the hand of all who hate us" (Luke 1:71). Jesus, the Head of the Church, is sitting at the right hand of God and He is ruling and reigning right now putting all enemies under His feet (1 Cor 15:25). Again, "The last enemy to be destroyed is death" (v. 26). The Christian Platonists are not seeking victory, they are seeking escape. Jesus did not tell us to pray "Our Father in heaven… your will be done in heaven when we get enough people saved and escape from earth" No, He told us to say "Our Father in heaven, hallowed be your name. Your kingdom come, your will be done, ON EARTH as it is in heaven." We should be more concerned about the Kingdom of God being "Left Behind" than ourselves being left behind. We must have a zealous passion for the advancement of God’s Kingdom in the earth and not just a fear of being left behind on earth
C. S. Lewis wisely wrote: "Aim at Heaven and you will get earth ‘thrown in’: aim at earth and you will get neither." The problem is that many Christians wouldn’t know what to do with the earth after it was "thrown in." In the parable of the ten minas it is said: "Well done, good servant! Because you have been faithful in a very little, you shall have authority over ten cities" (Luke 19:13). The problem is that many Christians, I fear, might reject the ten cities and say "oh no, this world is not my home; I’m just passing through. I can’t be involved with cities; I’m just waiting for the heavenly city." In the same parable it says "Engage in business until I come" (v. 13). Christ is coming back, but He has already gained the victory. It’s time for us to start acting like it. He is seated on the throne right now and "The kingdom of the world has become the kingdom of our Lord and of his Christ, and he shall reign forever and ever." (Rev 11:15)
We, Christians, look forward to a new heaven and a new earth; not just heaven. The thing that gets us through the hard times is not just heaven, but resurrection. "Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord. For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ and be found in him, not having a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God that depends on faith— that I may know him and the power of his resurrection, and may share his sufferings, becoming like him in his death, that by any means possible I may attain the resurrection from the dead" (Phil 3:8-11). Platonic Christianity sees our hope in escape from all things physical. The Gospel of the Kingdom puts our hope in resurrection and restoration. "For the creation waits with eager longing for the revealing of the sons of God" (Rom 8:19). Christians are not called to be mere survivors but more than conquerors.
The Gnostics hated the doctrine of resurrection. Some taught that Jesus only appeared to have a physical body. They could never believe that God would put on something as evil as human flesh. John warned about these Gnostics when he wrote, "For many deceivers have gone out into the world, those who do not confess the coming of Jesus Christ in the flesh. Such a one is the deceiver and the antichrist" (1 Jn 1:7). In eternity, we will not be disembodied spirits floating around heaven. We will inhabit our glorified, resurrected bodies as we enjoy the new heaven and the new earth. "The heavens are the Lord's heavens, but the earth he has given to the children of man" (Ps 115:16). "Blessed are the meek, for they shall inherit the earth" (Matt 5:5). As N.T. Wright said, "Heaven is important, but it’s not the end of the world."