The religion of the Ancient Egyptians - which is massively documented - provides a detailed picture of how the world of God's creation was before the work of Jesus Christ.
Creation was made by the pushing aside of chaos; civilization was like a clearing in the wild forest; and the chaotic forest was always trying to take back the world of religion, agriculture and the domain of the creating Gods.
Most of the Gods were Good, but the representatives of chaotic evil remained - such as Set (or Seth) who dwelt in the deserts around the fertile and civilized state of Egypt; and Apophis the primal world-serpant who, every night, attacked the ship of the sun, to try and prevent dawn.
Thus light/ life/ goodness/ order was engaged in a continual and eternal battle to hold-back the chaos/ evil that surrounded on all sides; and which would otherwise return the world to its primal disorder.
This may be taken broadly to represent the situation of divine creation on earth before the work of Jesus. And Jesus's work can be seen as the additional creation of Heaven, as a New Place to be inhabited by resurrected Men who have first been temporarily incarnated onto earth as mortals. The mortal state is that from-which each Man must choose Heaven - or Not.
By this understanding, Heaven is - and for the first time - a place that free men can inhabit where evil has been excluded - permanently.
By 'free men; I mean Men who are agents; operating-from their own distinctive divine selves; generating their own thoughts - mini-gods. In other words: In Heaven Men are secondary creators (operating within God's primary creation) - who can fully participate with God on the continuing creation of God's ongoing, expanding world.
Jesus gave Men the possibility of resurrection to eternal life. Resurrection means eternal bodies; and bodies can only be eternal in an eternal environment - which is Heaven. In other words, Heaven in a world without death.
By contrast; this mortal life we know, here on earth, is ruled by chaos (or 'entropy', dis-order). All changes and decays, nothing lasts unchanged; there degeneration and disease are everywhere and death is the inevitable terminus. This mortal world - taken in isolation - is therefore the same as that described by the Ancient Egyptians.
However, since Jesus Christ; we have the chance to opt-into Heaven; which is an everlasting world without evil - without chaos or entropy.
And at the same time, when resurrected into Heaven, we remain our-selves; indeed we become even more our-selves and able to participate in the ongoing work of God's creation.
So, our mortal lives on this earth give us all lived experiences of chaos, entropy and evil; and the opportunity to learn from these experiences in order to make a final, irreversible commitment in favour of Good.
In other words; mortal life on earth is what enables us to understand what is being offered by Jesus: eternal resurrected life in Heaven. And knowing (by contrast and implication) both sides, both possibilities... our free choice may be informed.
My understanding of this new possibility of heaven; is that it is due to the possibility of each Man making a permanent commitment to Goodness, to creation, to the work of God. Because Heaven is composed only of Beings that have made this permanent commitment - then Heaven is a place without evil.
All the inhabitants of Heaven (Men and others) are on the side of God and creation; and everything they (we) do in Heaven is in-harmony-with God and creation. Thus, In Heaven there is no tendency towards chaos, entropy, evil...
In another description; Heaven is based on the principle of love. The harmonious working of many free agents is possible by their mutual love. It is therefore love which is the principle of cohesion in creation - which 'organises' the work of many free individuals into a coherent, ongoing, creativity.
The 'process' by which any mortal Man from earth was made able to be resurrected-into Heaven was made possible by Jesus Christ; and the 'method' made simple and accessible. Since Jesus; anyone who wants Heaven merely has to 'follow' Jesus, who will lead us through resurrection and into Heaven (a path which he himself has taken) as The Good Shepherd.
It seems that (here on earth, in this mrtal life) not everyone knows-about Heaven, not everybody wants Heaven; and among those who do want to go onto Heaven, there are some who do not want to follow Jesus, or do not believe Jesus can or will lead us to Heaven.
But we can trust that God the creator will ensure that everybody will have the fullest chance to know such things sooner or later; and before each needs to choose between a commitment to Heaven - or Not.