That it is one approach to the oneness of religion known as perennialism, based on the premise that the true theology was taught in the beginning and has been gradually eroded. The Baha'i approach is very different. We believe that God revealed Himself progressively to various peoples in accordance with the age and needs in which they lived. The Tabernacle of Unity is an interesting dialogue between Manakji Limji Hataria, a Zoroastrian perennialist and Baha'u'llah.
http://reference.bahai.org/en/t/b/TU/
The first part is correct that when we were with God in the beginning, we knew the truth (it was not theology but) within us.
There was a crisis in Heaven which caused man to descend to his lowest ,and as we evolved from there, God revealed Himself in certain societies where there were good people, in order to create a higher culture ,which in time people would bring down to their own level of understanding
Many people have never reached the level internally where they can comprehend God .
To reach that level requires purity of heart and body, and to be seeking ,then God will come into that person, and they will evolve to a higher level .
Christianity developed from a Jewish Rabbi and is the last time God will appear on the earth before He comes to judge .Since Jesus came ,and as a result of of the suppression of Satan and his works for much of 2000 years we evolved our society to the highest level,, since we were banished from heaven .
Since things are now in descent, it appears that satan has been released ,and that people are now in the process of choosing ,God or the adversary .
Many christians think it will happen in an instant , but the descent is gradual ,until it becomes a torrent .
So the answer is that probably most people are incapable of entering into communion with God ,and make up their own gods in the vacuum .