Apart from the book 'Confessions' of Augustine, there exists the book 'Contra Faustum'. In this book Augustine rejects the learnings and convictions of a Manichean bishop called Faustus. It consists of 33 Chapters, each of them beginning with a statement by Faustus, followed by the refutations of Augustine, who had been a Manichean for ten years, but who had left the community and turned against it. We can read these texts both with the knowledge we now have about Manicheism generally, and in addition by reading the lectures of Rudolf Steiner on the subject.
By doing so, we can get a lively insight in the development of a separation between esoteric and exoteric Christianity. Rudolf Steiner characterizes this as follows (GA 65, p. 265):
'We could say, the human being who wants to come to a living together with the spiritual world out of his own human strength, really already was in a faustian form opposed to Augustine - not because his name was Faust, but in a true faustian shape - who said that the Manichean Bishop Faustus had the faculties to come near to the secrets of the world, by a raising of the human powers of knowledge. Goethe found, Letting the medieval doctor Faustus work on his soul, Goethe found a world that had in fact already delivered a judgment on this path of Faust. The judgment had been that such a human being must fall off the stream of humanity as a bad member, who wanted in this way to come to the secrets of existence through his own powers. Goethe did not agree with this view. It was clear to him that a human being can only be truly human, when he is able to fulfill the quest, although not in this old way as described in the 16th Century book about Faust. '
In the original book Faust is condemned because of his endeavour. In Goethe’s Faust he reaches Heaven...
The Angels(Soaring in the highest atmosphere, carrying the immortal part of Faust.):He’s escaped, this noble memberOf the spirit world, from evil;Whoever strives, in his endeavour,We can rescue from the devil.And if he has Love within,Granted from above,The sacred crowd will meet him,With welcome, and with love.(Poetryintranslation.com)Engel:Gerettet ist das edle GliedDer Geisterwelt vom Bösen,Wer immer strebend sich bemüht,Den können wir erlösen.Und hat an ihm die Liebe garVon oben teilgenommen,Begegnet ihm die selige ScharMit herzlichem Willkommen.(Gutenberg)
Augustine and Manichaeism II by Mieke Mosmuller