Answering this question forces us to reach back much further than recent Christian history. At the heart of this vision of the faith is a specific ontology, or understanding of what exists. If we roll back the years and peer at the very beginning of the Christian, and even proto-Christian community, we see (at least) two distinct communities coming together. At times their visions were synthesized and combined into a newer and more robust concept; but at other times they clashed, and one vision won out over the other. How does this inform modern debates both between Christians and non-Christians and, I think more importantly, within Christianity itself?
Christianity began as a Jewish movement. Jesus was Jewish, and so were all
Implicit in this debate was something less obvious, and of less immediate concern to the earliest Christians. Few of them had the training or time to engage in philosophical debate. But one of the big chasms between a Hebraic, or Jewish ontology, and a Hellenic, or Greek ontology, is their different understandings of the nature Reality at its most basic level. For Jews, there is the material world, and there is God, who transcends any normal conception of 'being'. For Greeks, however, there is the material world and there is a metaphysical world as well, what Plato called the realm of the Form. Additionally, there is an unknowable Source. This metaphysical reality contains something like a Mind or a collection of ideas which interacts with, but is separate from, the material world. Ideas, in this conception, actually exist as independent things, and they are made of a sort of very light, ethereal 'matter'. There are many, many implications to these two different ontological visions, but I'd like to focus right now on how these two visions affect our salvific theology, or our understanding of salvation and justification.
For Greeks, their ontology meant that salvation, as it were, entailed escaping from this material realm, which was crude and full of suffering. When Socrates drinks the hemlock ordered on him by the leaders of Athens, he assuages the grief of his students by assuring them that his soul, a sort of metaphysical spark, will ascend to or through the metaphysical realm to rejoin the Good or Source of existence (largely comparable to the Judeo-Christian God, with some significant reservations). I think everyone will immediately see parallels to contemporary Christianity: Christians claim that at death they will join God in heaven and enjoy the pure goodness of that realm.
But anyone who reads the Jewish Bible (which Christians refer to the Old Testament; Jews oftentimes refer to as the Tanakh) will note a conspicuous absence of any talk of going to heaven with God. Heaven is referred to in the Jewish Bible as the seat of God--but not as a place where humans go after death. The afterlife is actually little talked about in the Jewish scriptures. There are basically two strains of comment about it within its pages: one, there are many references to Sheol or 'the Pit'. This seems simply to refer to the state of nonexistence or decay that all beings experience after death. Later, the writers of Isaiah, Jeremiah, and other of the major prophetic works, talk of a coming resurrection--but it's important to note that they are talking about a physical resurrection, here, on earth, and a perfected Kingdom, also here on earth. There's nothing ethereal or metaphysical about that Kingdom of Heaven: it's the realization of God's will on this planet. It should be said that this vision is corporate rather than individual--salvation comes to the whole of creation, not just to particularly righteous humans.
So it becomes clear that the Hellenic, metaphysically dualist (not to be confused with theological dualism as seen in Manicheanism and Zoroastrianism) approach eventually won out as the dominant ontology of Christianity. Explaining why is well beyond both the space here and my own understanding, which is quite limited. But my own quick summary would argue that as the Christian community came to terms with the fact that Jesus was not returning imminently (which the New Testament makes clear was their assumption and hope), the promise of immediate glory in Heaven began to replace the eschatalogical (or 'end-of-the-world') vision that was both more Jewish and more in line with Jesus' teachings. The fall of the second Temple and the failure of the Bar Kokhba rebellion in 70 CE and 130-135 CE, respectively, probably reinforced this trend and spelled the end of Jewish Christianity (oftentimes associated with the Ebionites). But it's worth noting that a fully Hellenic ontology did not totally win out either. The more Greek-influenced forms of Christianity, like Gnosticism and Marcionitism, didn't survive much past the third century. The orthodox form of the faith that was agreed upon at the council of Nicaea in 325 CE was a synthesis of both strains. Christians have never stopped talking about the Apocolypse, or the coming resurrection. But these elements have been downplayed and the more personal approach to the faith has been emphasized, with promises of a sort of Elysian Fields dangled before believers.
So what, exactly, does this mean for Christians today? I think reanalyzing our ontology is critical to the continued relevance of our faith in a number of ways:
1. A more Hebraic ontology seems more consistent with contemporary science. Hebraic Christianity, as it were, does not demand any belief in a literal, metaphysical Heaven to which good people ascend after death; in fact, such a position violates the corporate, united understanding of salvation that is central to the Hebraic outlook.
2. This vision of Christianity is humbler, more compassionate, and less individualistic. Much of the arrogance and judgementalism that is both so unpalatable to non-Christians and, more importantly, so at odds with the life Christ demands of us, is less tenable under this more Hebraic ontology. If our salvation comes with the salvation of all creation, then we are all in this together. There is no longer a division between the predestined righteous and the evil sinners, condemned to Hell. There is only one body of people, all God's children, who must work together to build the Kingdom.
3. Hebraic Christianity lends itself to real ecumenical dialogue and progress. Christians who see all of creation as the recipients of Christ's sacrifice can begin to see Truth all around them. Not only those in other denominations of Christianity, but members of other religions and those who assert no religious faith whatsoever, are all our brothers and sisters. More specifically, the doors of reconciliation with Jews, who have for so long been oppressed, marginalized, and murdered by our Christian forebears, are opened ever wider under this vision.
I hope that shifting our vision to a more Hebraic ontology can both reform and reignite the Church. Instead of obsessing over personal morality, especially sexual morality, we can begin to see our job as participating in the building of God's kingdom in humility and penitence. This is, of course, not to say that personal morality is unimportant, but it should be balanced with a more holistic vision of what it means to follow Christ. As Paul says in 1 Corinthians, Jesus was the first fruits, and the general resurrection will be the rest of the harvest. We have work to do. Let's get to it.