Imagine there's no Heaven above us, no Hell below us. When John Lennon released his cry of confusion, many religionists took it as a dismissal of religious belief, among other criticism:

Interpretations of these lyrics abound, with some claiming Lennon was saying he was an atheist and other claiming that it was merely a condemnation of organized religion. However, if there is no hell below us and above us is only sky, it would seem as if Lennon is saying that some of the most important theological aspects of Christianity simply don’t exist! In short–I say atheist.

Wikipedia: Imagine: Recognition and Criticism
IxQuick web search: Criticism of John Lennon's Imagine

Whatever the song's author's beliefs or intent, I've always thought the religious critics missed the point about Heaven and, more especially to my thinking, Hell.

In the pre-scientific age of flat earth, where the sky and the heavens were synonymous, God and the angels sat among the clouds above, literally raining or hailing down munificence or punishment. Meanwhile, volcanic activity and geysers of hot water certainly lent credence to the belief in a fiery underworld.

Wikipedia

The idea of good and bad spirits was always around, but Zoroastrianism chiefly influenced higher religions with the concept of dualism, so I've read. The teaching parable of the Book of Job is a classic consequence. And there was that unpleasantness with a local senior administrator and his followers. But wherever we got the idea that the Evil One had power on a par with Deity, and held independent sway over his realm like a separate but equal Mirror Universe of Heaven, that's not monotheism. [Link unavailable 2019-04-30. Here's a dialog-free short version.]

Comes the Age of Space. We travel in the clouds and find only... clouds. We turn our telescopes to the farthest regions of Creation and see only... more stuff. We probe and explore the center of our globe and find.. only a remnant of the sun.

Old ideas of "where" Heaven and Hell exist could not stand. Quite naturally, their very reality therefore comes into question. That's why we sang, with John, "No Hell below us, Above us only sky." (Further apologetic for Imagine's lyrics awaits some other article.)

Moderns have managed to push the dual realms into some kind of science-fiction-like other-dimensions, but otherwise have not really upgraded the concepts.

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Let's start over, with God.

God creates universes. There really is a perfect, eternal universe centered around Paradise, home of the eternal Trinity, home of the immortals of that divine universe, and true home of survivors from time and space. Physically, from our perspective, it isn't "in" time and space, but the time-space creation circles that gravitational focus.

Just like in Star Trek V — Not!

That perfect creation is the pattern, the nucleus of all reality. We in evolutionary space are the mitochondria in one of the cells of the still-developing replications.

The kingdom, the government, really, the family of the Gods thus create life in abundance. Squishy, evolving, fallible life like they can't grow in the perfect place. They make children of God out of... dirt! out of... meat! Believing creatures who have to learn to be spiritual! From the perspective of those never-erring Eternals, who never grew up or sinned, our partiality of perfection must be astonishing.

They put in place mechanisms for the continuation of mortal personality beyond material death, an accumulated real thing which reflects the spirit's efforts to bring animalistic thinking into harmony with divine values - a soul by which you can be reconstituted in the mansions of resurrection. It's taken care of. They even sent us that message, in the most powerful possible Way.

The true dualism is, a soul survives, or there is nothing of survival value. Much breath and ink has been expended debating whether all are saved, whether judgment comes soon after death or at the end of an age, what one must do to be saved, and whether every soul arrives already perfected and saved, or some (most, it looks like from here) need a purgatorial extension before being able to make the fully-informed free-will choice to join the eternal family. All these weighty matters lie beyond our present scope, because the question at hand is not the way of Heavenly salvation, but the consequences of the Other Choice.

Dualism is an illusion, merely a subjective binary interpretation of the quantity of water in a glass; fullness is the reality by which less than full is considered, emptiness being a total lack. Cold is lack of heat, but unless you're at absolute 0°K, there is some "heat." Darkness is absence of light. Ignorance is the absence of knowledge. Immorality is the absence of a heart guided by wise fellowship. The absences, lacks, and emptinesses are not "real" as much as they are defined by lack of that which is real - heat, light, wisdom, love.

Those who reject the light do not go to a fiery pit and burn in eternal torment. It pleases our animal thirst for vengeance, for old-fashioned, Old Testament justice, to imagine the worst souls writhing in agony eternally for their iniquities. But in mercy, the iniquitous simply cease. They are, in Pythonian, ex-souls. There is no longer anyone there. Personality disruption is complete. Is that not heartbreaking enough for the family of souls to endure?

Jesus spoke of those who rejected the truth as being cast upon Gehenna. Some take that to mean the Hell of their own concept, but Gehenna was the perpetually-burning trash heap (tire fire of its day) outside Jerusalem. He was saying, my way or the trash heap.

This only concerns Hell as a location in reality. There is a need in some folks for fear of eternal torment; for them, until the carrot of love of God, fellowkind, and values replaces the stick of fear, avoiding eternal torment is a positive motivator that understanding of mere eternal cessation may not provide. Then there is the metaphorical living Hell of separation from God, the burning torment of divided loyalty, a life of sin. And there was, likely still is, a real Devil, walking this world, who brought a kind of Hell to our world, not yet repaired. But again, all these are beyond the current scope. In practical terms, a soul has a simple, root choice:

Survival or not. You might say, Join or Die.

Heavens, yeah.

Now go forth, enlightened, believing firmly in the Heaven you get around you every day, the Lord you find in the eyes of every struggling fellow mortal, while assured that, although there is no Hell, the cartoons about the guy with the horns and hooves and the jokes about who's there or not can still be funny.