Modern life extension is generally regarded as A Good Thing, and perhaps the greatest triumph of our civilization. The usual reasons given have to do with medicine, public health and societal changes; but maybe the real reason is spiritual - and negative.
Maybe so many modern people live so much longer because they have failed to learn the vital spiritual lesson/s for which they have been mortally incarnated. Some lives have perhaps been mercifully extended (by divine intervention) because if they were to die at the normal time, such people would choose hell.
In such a pervasively evil world as the modern West; an extended life perhaps gives such people more chances to awaken to the realities of their existence, and make an active decision to accept the gift of Jesus.
What, then, of the poor physical health and high prevalence and severity of dementia that so often accompany advanced age? How might that benefit the eternal destiny of those individuals who suffer such things?
To speak in gross generalisations - applicable only to some instances - the experience of physical and mental degenerative disease strips-down life, simplifies human experience, in what may be a very stark and extreme fashion. Adult (pseudo-) sophistication is dissolved. A person may be reduced to absolute dependence. Ideologies and interpretations are lost.
It may be that, under such circumstances, a human soul might - for the first time - perceive the basic human condition with a clarity that was never attained during earlier years of health, vigour, ability; pleasure, comfort and prosperity; distraction and temptation.
If so, this would indeed be a harsh lesson, and a suboptimal way of teaching and learning. Nonetheless, Men are often such that kind teachings are rejected and only harsh lessons are learned. When we repeatedly and scornfully refuse to learn under optimal conditions, it is a mercy if we are allowed further chances, in different conditions - perhaps exactly the condition best tailored for our-selves.
In sum; the reason why modern people live (on average) much longer than previous generations of humans may be because we are (overall, in an average way) the most evil generation of Men ever to inhabit the planet.
