Qualities of the human body and its psyche evolved to give an evolutionary advantage and so be more likely to be passed on and normalised.
There is a moment between sleep and wakefulness when a commanding voice may be heard, coming perhaps from a drama from further back in the dream. It seems to be the sudden intervening authority of an awesome power.
Without the benefit of the hard headed skepticism which we have also evolved as a species, it could only be as it seemed – presence and voice moved though a veil from another world.
The digestive parts were perhaps at war with each other sparring and gurgling while the sleeping brain for its part had tried to withdraw amid troubling fears of relationships with loved ones and always lurking death.
After that moment, imagine how his authority and importance now swelled up to impose various doctrines and religious themes born for the adherence of others.
The whole charismatic show for a thousand years collapses apiece if you take away that moment he mistook his own mere inner voice for the interactions of a god.