The Brethren of the Free Spirit believed:
1. God is both immanent and transcendent, present in all of creation, including humanity.
2. history is divided into three periods, each corresponding to a different aspect of the Trinity:
- the Age of the Father: the era of the Old Testament (Abraham, Moses and the Prophets etc)
- the Age of the Son: the coming and ministry of Christ and the ensuing era of Christianity
- the Age of the Holy Spirit: the era now (then) coming to pass, when God becomes manifest in Man.
3. through direct experience of God, the Holy Spirit flourishes in the individual soul, and man can achieve a union with God whereby he no longer sins.
Those who achieved this state of being - of mystical union with God in this lifetime - were called 'the Spiritualised'. They saw themselves as having evolved beyond ordinary states of good and evil (duality), replacing notions of faith and hope (beliefs in things which might be) with the positive light of knowledge (Gnosis, or direct knowledge of God). This union with God was achieved through an austere process of self-abnegation and annihilation of the ego.
So, the world was seen as on the brink of a vast transformation of consciousness, in the last days before the dawn of a new heaven on Earth. In this new Third Age, the Christian burden of original sin would be lifted from humanity, and love would rule. All people would be naked and unashamed as they had been in Eden. They would live without sorrow or labor, and all wealth would be shared freely.
Accordingly, group worship in the nude was standard practice in most Free Spirit circles, as was promiscuity. However, as recurred in our own brief "flower power" movement of the late 1960's, the drive for spiritual self transformation was too often lost amid ego-stoking self indulgence.
But, despite the efforts of the Catholic church to exterminate the "heresy", the Free Spirit remained an active presence in European culture for at least five centuries, and its influence lasted longer still.
adapted from Wikipedia and John Michael Greer