As per my other post, having looked at some of the problems with both dualism and monism, I will try to articulate a way forward. But before getting in, I will define my terms, briefly, again.
Monism is the idea that sees Oneness over all difference. This might be because difference is an illusion, or a problem to be overcome (whether by man or God). No orthodox form of Christianity (i.e. accepting an infinitely qualitative Creator-creation distinction) is strictly Monistic. However, certain forms have tended this way by either adopting a form of Pantheism or Panentheism. There are also movements that have sought to collapse all difference in Creation through conquest or certain eschatological theologies.
Dualism is the idea that sees a strict, sharp, and thick dichotomy between things. Certain forms of difference become permanently fixed. Sometimes this borders on a kind of Manichaeism (i.e. equi-potent forces of Good & Evil, God & Devil) or theologies of the Wholly Other between God and Man. This sprouts up throughout Christian theology commonly, and is the vague framework most confused pop understandings use for Christian theology.
As one can see, both sides have things going for them. What I'm offering is the idea of Duality. While similar to Dualism, the difference is in the permanence and sharpness of the line that separates. It also accounts that not all difference is division, that features may complement and be together yet separate. Thus, one might say that Duality is a soft form of Dualism, but I'd hesitate on that. Dualism tends towards polarities, while duality will tend to reveal symphony, synthesis, cooperation, participation, and interaction. Instead of trying to define a principle of duality, I will give examples throughout the Scripture to highlight what I mean.
The First: Creation. When God created, He set up many boundaries between certain realities. He set darkness from light, waters above from waters below, land from water, beast from man. While these boundaries exist, they can be traversed. In fact, the hope is a rightful kind of transcending of boundaries. But more often than not, these boundaries are transgressed. The wickedness of the Earth invites the flood that wipes out all of Mankind (except Noah and his kin). Man's sin makes him more bestial, worshiping his belly as god, among all sorts of other beasts. Thus the boundary is permeable.
The Second: Man & Woman. God separated the Woman from Man's side as a suitable partner. This is the beginning of sexual differentiation and marriage. Despite modern advocates, genders are binary. However, as is true and now a dominant belief, genders are cultural. Men are not born male, and women are not born female; these are genders to grow into, as a sign of maturity. The border is permeable, and as per creation, sexual confusion is a kind of creational confusion. This ought to be the prime argument Christians used to explain marriage and justify the particular gender duality. Of course, most modern advocates for LGBTQIA+ decry the notion of created sexuality and God's intention for not only men and women, but also male and female. There is not merely one or the other, but it is something one must become, but become as per the pattern of Creation. The boundary is a permeable one, for both ruin and glory. I will return to the latter later.
The Third: Israel/Church: When God called Abraham, and blessed him with the promise of seed, this was the foundation of Israel, the holy people of God. Israel was separated from all the other Nations, and given temporary Sinai-Torah proclamations about how to police this boundary. Of course, Israelites might forsake this and begin to act like the Gentiles. This did not make them not Israelites, but Israelites who sinned. They were called to something, and rejected it. The boundary, as the borders of Israel, were permeable. Israelites were not immediately cut off for their sins, acting contrary to who they were, even if they were met with judgement.
But lest we forget, Israel was tasked with a mission. Israel was distinct, but was to operate as a Priest for the Nations. It was to Israel that others would come, and eventually lay down their treasures in the Temple and worship the True God. The destiny for Israel was transcending of the boundaries, where the other nations would come in. Israel was to eventually blur the boundaries, and such is the function of Israel's transcendence into what we commonly call Church, the Body of Christ. Christ is the fulfillment of Israel, an Israel in the Flesh, who broke down the boundaries in His body. In Him, the border is transcended as Israelite(Jew) and the Nations(Gentile) are gathered in as One. Now the boundary is fuzzy, but distinction still remains, as Jews still the one's to whom the promise was given.
As per the above examples, all of Creation is to be united, while maintaining distinctions. The sexual differences of gender are not to be erased, but transcended in their incorporation into Christ (no male or female in Christ). There is no more division, even if there remain distinction. Thus while we will remain men and women, we will not give or be given in marriage in the Resurrection. The old order of things will come to a conclusion as we enter into another age. These blurring of boundaries, distinction without division occur elsewhere.
The Fourth: Heaven and Earth. Creation was divided into Heaven and Earth, or as we might conceive of it, spiritual and physical. However, it's perhaps less helpful to think this way. In a Dualistic paradigm, matter is of a fundamental different nature than spirit. But perhaps not. As St. Gregory of Nyssa postulated, and modern physics is coming to grips with, perhaps the differences between energy and matter are not so different after all. It has to do with "density" (something Christians who reappropriated the Platonists knew).
What we know as physical matter is just "heavier" and "thicker" than what we know as light and flame. And perhaps as others have considered, Angels and the realm of Heaven are a more refined matter that possesses more refined bodies. Of course, God dwells in Heaven, but He is beyond Heaven as well. He dwells in both Heaven and Earth, and beyond all created realities. In the Parousia, Christ will reunite Heaven and Earth and the current boundaries will blur. Heaven will descend down to Earth in the New Heavens and Earth. Distinction will remain, but we will be blessed with spiritual bodies, material of more refined essence. St, Origen nor other Christians who utilized Plato and other Platonists were not Gnostics. They actually might have grasped created reality better than the Modern age has.
The Fifth: Logoi and Created Things: This is a kind of addendum of the previous topic. However, a question that has plagued philosophy is whether or not things are "Real" or are nominal. In other words, does a "Tree" really exist or are the collection of things we call trees just a Human convention for similar, but different, discrete objects? While this is not a big deal, when it comes to the big transcendentals (Good, Truth, Beauty) it gets dicey. We're prone to get gored on Socrates(Plato)'s Euthyphro dilemma: are things good because the Divine Authority says so, or does the Divine Authority say so because they are good? The former makes them arbitrary (and the side many Christians would rather get speared on), the latter makes the Divine Authority unnecessary (and actually rather creaturely). Of course, many philosophically astute Christians would say that God contains the transcendentals. But the paradigm of duality helps make sense of this, as individual instances of the Real make them not merely simulacra (illusions to be overlooked to see the Real). Why does this matter? Because when God created, He did not merely randomly compiled molecules, but had a plan for the Creation (thus the things pre-existed in the mind of Christ, the Logos). However, as they participate, they have an independent identity from the Real. Thus, things can participate fully or slip away. The dying of the Created order reveals the blurring of boundaries as things cease to be the Real things they are intended to be. But, in Christ's return, the groaning creation is to find unity with the Heavenly Ideals from which they draw being. This section is for the more philosophically inclined, but it's worth further reflection.
The Sixth: Heaven and Hell: I don't like these terms, but they are so common. I'd prefer, as per Scripture, the Resurrection to life and the resurrection to damnation. But, of course, what does damnation really mean? I am relatively agnostic on this, not wanting to get into the debates over the nature of Hell. However, if we appreciate an eschatological erasure of division without distinction, we can posit some theories that have circulated. Will damnation be eternal destruction, a closing of the door upon the age with those who've rejected Christ locked on the other-side. Does this mean obliteration or what? As per N.T. Wright, are the damned locked into the bestial state that they've chosen? Is damnation eternal, but the ability to cross not (i.e. like C.S. Lewis's The Great Divorce or George Macdonald's Lillith)? Could there be still a hope for a final salvation of all, even the Demons? To dogmatically rule on this is foolish, as Christ is rather adamant about judgement. Those who refuse the life of mercy, to reject Christ's Second Adamhood and the restoration, and transfiguration, of Human nature, refuse the destiny of Man. But thinking this through, with tentative thoughts, suffused with hope, ought to be considered carefully.
The Seventh: God and Man: As per St. Athanasius, and others, God became Man, so Man might become a god. The idea was not a confusion or erasure of the infinite Creator-creation distinction. Far be it! Rather, it was that Man transcended his own nature in his nature's transcendent calling as Image of God. Thus, man is opened up infinitely towards an Infinite God. We move towards God infinitely, even as He is Infinite and can meet us in the distance. This is a way to get around the problem of either man being eternally distant from God or the seeming problem of collapsing Man into God. It's hard to imagine distinct men and women in Paradise, while also saying that we are united with God and become "partakers of the Divine Nature" (as per St. Peter). We truly see God as He is, but that does not mean we become erased in the process. As radical as it might seem, we become sons of God by grace as Christ is the Son of God by Nature, per Maximus. This might need to be qualified depending on who you are talking to, but it rings with truth. If Christ is fully Human, there our Human nature, like His, becomes transfigured for our own individual personal instantiations of it.
I hope this clears up, somewhat, what I'm talking about. The above are all reasons why Duality, and the distinction without division, remains very important. Not only does it avoid philosophical problems, but it provides a logic for Christians trying to answer difficult questions for our modern age. It has import for thinking and talking about homosexuality and marriage, Christian hop and the resurrection, spiritual realities (angels, demons, etc.), the Church and the State, and many others. In fact, it's sort of applying Christ's hypostatic union (100% Man, 100% God, together, without confusion but without division) to created realities. It shows how, perhaps, Christology is not foreign to the rest of the Scriptural narrative, but also helps one understand it. Reworking St. Augustine's formula, Christology, revealed in the New Testament, is hidden in the Old Testament.
I hope this is a helpful paradigm.