It seems like no more than common sense that humans would function better in this mortal life by concentrating on this mortal life and ignoring spiritual speculations - but it is not true.
When humans started to believe that biology explained Man, they found themselves demotivated so profoundly that they have almost stopped reproducing - and have stopped even wanting to have children.
So biology thwarted biology.
It might have been thought that common sense would work better if unfettered and unconfused by 'theology' and 'religious mumbo jumbo' - yet we live in a society where the absence of common sense is so extreme, that experientially-obvious falsehood and frankly delusional psychosis is, more every year, enforced by the government, law, rulebook and media.
Clearly, if Man fails to consider his mortal life in the wider perspective of survival beyond death, then he becomes so confused and demoralized that he will lose even this mortal life.
When Man fails to interpret his function in a religious perspective, he will lose his grasp of even the bare concept of functionality.
It seems the natural must be sustained by the supernatural - and now we know this maxim is not just as a theory, nor a Chestertonian paradox; but we know it by direct personal and civilizational experience...
Except that the truth of the maxim is being daily confirmed by the very fact that we fail to see and comprehend those proofs which lie so abundantly scattered all around us, and inside our despairing souls.