The Platonic/Plotinian teaching is pure idealism, even if it is expressed in a vocabulary and language that we may not immediately understand as such. (Incidentally, 'matter' is a very misleading translation for the Greek hule in Plotinus. In Plotinus, it carries none of the connotations of 'matter' in the modern physical sense, but is rather the extremity or principle, so to speak, of non-being, of darkness, of nescience. I have toyed with the idea of using 'anti-stuff' as a translation for hule.) There is only knowing, experience, 'mind', 'consciousness' or, as Plotinus puts it, contemplation. All is, as Plotinus says (Ennead 3.8), contemplation. The One is complete pure knowing or contemplation beyond knowing/contemplation. Nous is already lesser, incomplete, impure, adulterated to some extent but still unified knowing/contemplation having already been mixed, so to speak, to a certain extent with nescience/darkness/non-being, which Plotinus sometimes refers to as noetic hule/'matter'. Soul is knowing/contemplation mixed to the greatest extent with nescience/darkness/non-being to the point that it appears as individuated as our souls and in space-time and sense-perception, etc. It is still, though, the same knowing/contemplation, in its reality unchanged and unalterable and indestructible, as knowing/contemplation is still only in itself purely knowing/contemplation as such and can't be anything else, but is now turned or looking in the direction of the extremity of nescience/darkness/non-being and thus no longer knows itself or complete pure knowing/contemplation. The soul, thus, needs to turn around back to, to redirect back its attention to, to regain the complete pure knowing/contemplation of and that is the One, to re-become that complete pure knowing/contemplation without any admixture of nescience/darkness/non-being. Thus, renunciation and asceticism is of the very essence of the purification process, and also is not just of instrumental value but remains of the very essence of the fuller knowing/contemplation state(s), since involvement in and pursuit of the world of diversified individuated sense data in space-time more than is absolutely necessary, which is what worldly life is, is the very fact of looking in the direction of darkness, of only knowing/contemplating in a very darkened, impure, incomplete, ignorant way--being in worldly life is by definition knowing/contemplating/seeing the darkness and non-being of sense perception. The practice of purification, on the other hand, is more and more only seeing/knowing/contemplating the Forms and Nous and then the One/Good, and thus being in the very state of Nous and eventually the One Themselves, and thus obviously involves knowing/contemplating/seeing worldly life and its things of the senses less and less. The One is, of course, always there and unchanged, but we don't know it without turning away from the sense world, which is really non-being, in both life and mind, and turning the imperishable knowing of the soul back to the One.
