@Ghazali
I dont know but your style of writing seems to be pretty much inspired by the colossal reformer of Islam Imam Al Ghazali Alihi Rehma, the likes of which mankind has never seen before and even after more than nine hundred years of his demise.
Coming back to your complex questions which I think is not that easy to answer. Anyhow according to my limited understanding Prophet SAW referred a term Fitra which obviously is designed to recognize truth from falsehood, merit from demerit acts and reality from illusion.
Imam Al Ghazali AR himself became mentally ill when he tried to search some critical questions related with the nature of reality and when all of his mental faculties became exhausted then God Himself cast a tiny spark of light on his heart and only then he was able to relax.
This allusion of Casting of Light from his autobiography Munkad Fil Dalal (Deliverance from an Error) do indicate the importance of external factor in the shape of Gods mercy duly complemented by the pristine Fitra of Man. The critical point is this Fitra / undulated nature of Man which normally Man has to attain once it has become corrupted and unclean by committing sins in his life.
Intellectual capacity is pretty much limited in its scope to determine sound nature from unsound, the fact which is evident in this current era as well, it is pretty much evident from the trail of disintegration since the Western world has embarked on the journey of material sciences devoid of divine wisdom and guidance. But with all of its limitations mental faculty do has its due place in the search of reality and it has to follow the guiding pointers of pure human spirit.
Wallahu Alam bil sawab.