The materialism (aka. positivism, scientism, reductionism) that swept the world over the past centuries - but especially from around 1800 with the industrial revolution - had several devastating effects on Man's assumptions.
Men lost sight of some key pieces of knowledge that were of vital importance.
Unbelief in God, and that this is a created reality, are two well known losses; but others are also spiritually lethal.
One is the insight - dating at least from the Ancient Greeks - that our mortal life in this world cannot ever be satisfactory.
The insight that a world characterized by change, decay, and disease could never, under any circumstances, be wholly satisfactory; used-to-be so obvious, that to argue for it would have been regarded as silly.
This understanding included that a life which ended in our death (and the death of everybody and every Being we knew) was by that unavoidable fact inevitably and fatally flawed.
Yet, by the middle 19th century and for another century, the intellectual world was filled by ideas that aimed (whether explicitly or covertly) at creating a utopia on earth and this mortal life!
The insight had been lost, therefore the impossibility was simply denied.
People were busily engaged in adapting or inventing 'new religions' (or replacements for religion) which tried to implement all their wishes in this mortal world, 'forgetting' what the ancients had always known - that the nature of this world (and our-selves) is such that utopia, perfection, our ideal life - is intrinsically impossible (in this world).
The best that could be devised was that Men might evolve or develop a kind of consciousness for which the unsatisfactory nature of this world was obscured and deleted from awareness; that Men should therefore aim (by one means or another) become completely happy with an evanescent world of disease, degeneration - and death.
In effect; this required a reduction in consciousness and a loss of humanity; although it was often advocated as a higher consciousness and a step toward divinity! (Often by deploying a distorted misapplication of ideas selectively-drawn-from Hinduism, Buddhism or Sufism.)
In other words; intellectual culture, and indeed the spontaneous awareness of the masses, lost sight of the fact that this world can only become satisfactory in the context of Heaven to follow.
The intrinsic problems of this world, which are fatal to human gratification if this world was indeed everything; can be understood as positive and beneficial 'learning experiences'; but only if an eternal Heaven comes after.
This reached such a pitch that even Christians downplayed the importance of the central promise of Christianity - of resurrected eternal life - and began to focus more and more exclusively on the moral benefits of Christianity - as they may be revealed in this world.
Christianity began to be seen as essentially a morally-enhancing religion: as a means to the end of improving individual and social morality.
Even so great a Christian as CS Lewis said it was better if Christians did not think too much about immortality, but became Christian for other reasons primarily (mostly moral reasons).
Lewis himself converted to Christianity before believing in the reality eternal Heavenly life; and he regarded this as A Good Thing because he felt that the alternative was to convert from mere terror of death.
The need for an eternal perspective came to seem childish, immature, selfish - rather than a plain metaphysical necessity for understanding this mortal life. Somehow, Christians were supposed to reconstruct their faith such that resurrection was 'an optional extra' rather than at the very core of the faith!
In time this world became, therefore, firstly more-important-than the next - and finally all-important; so that now many/ most Christians base their religion in this-worldly and political projects.
(This led to the convergence of Christianity with Leftism, then - as of 2022 - the absorption of mainstream Christianity by Leftism.)
And the loss and dissolution of 'the self', of our distinctive personal nature; even the post-mortal loss of body (instead of resurrection) - instead of being regarded as an intrinsic flaw to be superseded by Resurrection into Heaven - became regarded as actually definitive of the highest spirituality and mysticism: even among Christians!
Such deep errors have by-now so thoroughly pervaded modern mainstream culture; that the real Christianity rooted in Resurrection and eternal Heaven has come to seem almost bizarre, eccentric, foolish.
We have now all-but lost the convinced utopianism of the late 19th and early-mid twentieth centuries, so that a mood of nihilism and despair has settled onto the mass of Men - and has driven them literally insane.
Consequently, we are living through a purposive and advanced strategy of global self-destruction masked by the thinnest veneer of oppositional socio-politics - sustained by a relentless shallowness, triviality and refusal to think about the fundamental and false metaphysical assumptions upon which our entire public discourse is constructed.
Few can perceive the once obvious truth that these mortal bodies and this mortal life are - even at best and most ideal - a transitional phase; necessary but not final.
Therefore, it has become extremely difficult for people to recognize what was once obvious - that the only full and coherent answer to the fundamental inadequacy of mortality in this world; is Christian Resurrection into Heaven.
This is why Blaise Pascal in his Pensees correctly stated that all Men would - if only they understood it - want Christianity to be true.
And that is the proper basis for Christian conversion: to want Christ's promises of Resurrection into eternal life in Heaven to be true; and then to discover for oneself that it is true.