I have often come across variations on the theme that this world and the Men, animals and plants who dwell here are perfectible: that this mortal life can be transformed into Heaven.
The transformation has been variously expressed; one idea is that the gross materiality of bodies will be transformed into light; or that matter becomes spirit; or (in New Age type thinking) that the vibrational-state or frequency of the planet and everything on it will be raised.
The underlying idea seems to be that this world as-it-is is "entropically" subject to death, decay, disease, and sin; but that the corruptible "stuff" of mortality and imperfection can be transformed and replaced by in-corruptible stuff... Thus Earth is changed into Heaven.
I regard this metaphysical belief as an early manifestation of Mankind's alienation, of our diminishing participation, of the loss of primal "animism" by which we knew that this reality is constituted by Beings - loving, conscious, purposive beings - and these are the bottom-line explanation.
Because reality is Beings - therefore restatements of ultimate reality in such terms as vibrations or frequencies, of matter-spirit distinctions, or of light or any other physical property - are all abstractions. (All "physicsy").
That is these ways of understanding reality are all distanced, symbolic, representative - but not reality itself; and only a secondary form of understanding.
If, instead, we embrace the original and spontaneous human understanding of reality in terms of Beings, then we can recognize that what prevents Heaven on Earth is not a matter of matter, not about the "substance" of this world (as if it could be separated from the spirit). But instead that death, sin, insufficiency, "entropy" are a consequence on the inharmoniousness of relationships between Beings.
In a nutshell: it is the lack of complete and eternal love that prevents our eternal lives and Heaven.
We must rectify relationships and enable eternal Love to have Heaven.
Heaven can arise only by Loving God first - that is, recognizing and committing ourselves to God's creation and creative methods and purposes.
And second: by loving our neighbours/ fellow-Men - in other words Loving All Other Beings - forever.
These are the two Great Commandments articulated by Jesus Christ; and can be seen as shorthand for the eternal and irrevocable commitment to live by Love; in harmony with God's creative will.
When beings live by Love, this is eternal - because there is nothing in Heaven (thus conceived) to disrupt or destroy divine creation.
Since Love is what is needed, and since Love is a choice - we need to recognize that Love is the free act of a Being with agency as an essential attribute.
Therefore (because Love cannot be imposed, top-down, from-externally); everlasting life and Heaven cannot be imposed, but must instead be chosen: indeed there must be a commitment to live eternally by Love.
To make our lives eternal and dwell in Heaven is therefore a matter of relationship, and that relationship is voluntary (again, Love cannot be imposed)...
Thus Heaven cannot be imposed on Earth by any means - what must instead happen is that all the beings of Earth (including the being of Earth itself) must choose to live by Love.
I cannot see any way that such a lot of choices would be simultaneous, and Heaven cannot be partial; which would seem to mean that either Heaven must be delayed until every Being has chosen it -- which delay seems contradicted by Jesus's teachings (esepcially in the Fourth Gospel - of "John"). Or Heaven is elsewhere.
(And also there is the fact of at least some apparently eternally-self-damned demons; which would prevent Heaven ever from happening - if indeed all must repent before eternal life can ensue.)
Heaven surely cannot be partial; because the dwelling in Heaven of selfish or cruel Beings would not be Heaven! It would lead to destruction of that Loving creation which enables both perfection and eternity - and is itself the state of Heaven.
So, it seems to me that Heaven, and our eternal resurrected life therein, must be elsewhere than this earth; and segregated from this world of sin/ death - such that those Beings who have not committed to Love, do-not and cannot affect Heaven.
My understanding is therefore that this-world cannot be other than it is; which is a consequence of God's Loving creation in a context of primal chaos, creation in the context of Beings that all have some tendency to death, to selfishness, to sin (and some Beings apparently incapable of Love).
This world is temporary, and creation here is like the rule of a wise and wholly-Good parent imposed on children (i.e. Beings) who vary in their innate degrees of Goodness, and obedience.
But for eternal life and Heaven to exist, these Beings (us, you and me, included) must be released from obedience in order to choose freely whether or not we want Heaven.
So, this world is mixed: and has in it both evil (primal chaos, entropy, selfishness...), and also Good - vast and renewing manifestations of God's creative Love.
Therefore; every Being or entity in this world has direct and personal experience of evil and Good.
Every Being in this world is in a position to make the eternal commitment to live wholly by Love in a wholly Good "other place" that is Heaven - a Heaven that already exists, and to which we each can go by following Jesus Christ through resurrection, after death.
In other words; we can, will, and must choose either Heaven; or else "more of the same, mixed, kind of thing".
But this world is not staying the same.
This world apparently accumulates evil through time, because evil just-is cumulative, and Beings that choose evil become more evil..
(Unless the Beings repent; which means precisely making a commitment to follow Jesus to Heaven.)
Also; Beings that commit to Good are incrementally being removed from this-world and segregated in Heaven.
In other words; this mixed world already contains Hell in part and in places; but is becoming more Hell-ish with time.
In conclusion; Beings such as our-selves can choose Heaven or Hell - both of which we all have experienced in this mixed world. This is the choice between eternally living only by Love; and not making this commitment.
We can choose Heaven, or we can choose to reject Heaven.
We can also choose to "delay" our choice -- but this is, in its actual effect, a here-and-now rejection of Heaven, and embrace of this mixed-world, which is tending towards Hell.
We can go-back on this rejection of Heaven at any time: repentance is always open to every Being.
But, in this mixed but evil-accumulating world, and given that un-repented evil will become more evil; delaying the choice of Heaven does make salvation more and more difficult.
Repentance is never impossible, but always gets more difficult with delay.