Rudolf Steiner speaks of this in his lecture The Bridge between the Ideal and the Real:
Augustine passed through the impressions of the most diverse world views.... Above all, he passed through Manicheism and Scepticism. He had taken all those impulses into his soul which one gets if on the one hand one looks at the world and sees everything as ideal, beautiful and good, all that is filled with wisdom- and then, on the other hand, sees all that is evil.
Now we know that Manicheism tries to reconcile these two streams in the cosmic order by assuming an eternal polarity, an everlasting dualism, between darkness and light, evil and good; that which is filled with wisdom and that which is filled with evil.
Manicheism comes to terms with this dualism in its own way, only by uniting certain old pre-Christian basic concepts with its acceptance of the polarity of world-phenomena. Above all, it unites certain ideas which can be understood only when one knows that in ancient times the spiritual world was perceived by humanity in atavistic clairvoyance, and perceived in such a way that the content of the visions resembled in appearance the sense perceptions of the physical world.
Now, because Manicheism took into itself such ideas of the physical 'appearance' of the supersensible, it thereby gives many people the impression that it is materializing the spiritual, as though it presented the spiritual in material form. That of course, is a mistake which more recent views of the world have made, a mistake even made by Theosophy [and by modern Spiritualism].
Augustine actually broke with Manicheism because in the course of his purified life of thought he could no longer bear this apparent materializing of the spirit.
As Augustine said:
"I fell among men who held that the light which we see with our eyes is to be worshiped as a chief object of reverence. I assented not: yet thought that under this covering they veiled something of great account, which they would afterwards lay open."
Mani taught an essentially monistic system:
De Vita Beata. Pref.
"Manichaeism is a monistic system. For the Manichee, there is only one universe and it is man himself who has divided it into two: the perceptual and the conceptual. And it was within man himself that Mani sought a bridge between the world of the senses of the body, and the world of the spirit.
He found it by integrating the senses of the body with the senses of the spirit in order to reveal within all terrestrial phenomena the spiritual reality which fashions and sustains them. In such a manner, Mani perceived that all human beings were themselves sun spirits.
He taught his followers how to be reborn on the spirit and how to live in accordance with the life of Christ during his three years in a physical body on earth (that is, from the moment of the baptism in Jordan to the death on the cross at Golgotha.)"-Trevor Ravenscroft