“The soul or mind is the seat of all imaginative representation—both the higher representation … and the lower. … It is equally certain that all that follows upon the mental act or state, the disturbance, confined to the body, belongs to the sense-order; trembling, pallor, inability to speak, have obviously nothing to do with the spiritual portion of the being. The Soul, in fact, would have to be described as corporeal if it were the seat of such symptoms. …
“No Ideal-form can be the victim of disturbance or be in any way affected; It remains in tranquility; only the matter associated with it can be affected by any state or experience induced by the movement which its mere presence suffices to set up.” ~Plotinus
Soul or Mind
Plotinus seems to be saying in the first line that “soul” and “mind” are just two different names for the same thing. I don’t really know if that is the way he meant it, but if so, he is wrong. Soul and mind are definitely not the same thing and imagination is a mind game not played by the soul.
The rest of the quote may be difficult to follow, but essentially it is saying that the soul cannot get sick, disturbed, angry, jealous, or any other negative emotion or state. Those are things of the body and mind. But here is the rub: while physical illness cannot really affect the soul, spiritual illness can affect the mind and body.
The famous myth of Sisyphus, where he is punished by having to push a large rock up a mountain side, only to have it always roll back down, may be an allegorical representation of this. It is almost impossible to push the rock (material problems) all the way to the mountain top (Soul), but it is quite easy for problems to roll down to lower levels. So problems on the spiritual level can flow down to the psychic and mental levels, and mental problems can lead to physical ones.
You might think there can’t be spiritual illness if it is true that the soul cannot be affected as Plotinus says, but when dealing with things on the spiritual level, the rules and laws are different on the lower levels. You might think of it this way: the soul is surrounded by a protective shield that reflects problems away from it and down to lower levels. Any problem sent up to it simply bounce off, any problems that come down to it keep going down without damaging it.
There is one exception of sorts. If the person commits a truly heinous act such as murder, while the soul is not actually harmed, it feel something similar to great pain. As a result, it will often separate from the physical body that is causing the problem and return to the spiritual realms on its own. This leaves behind a physically living, but soulless zombie. So spiritual illness is a serious matter.
Plotinus adds that no “Ideal-form” can be the victim of disturbance. That is, the Ideal Form cannot be changed by negative or evil acts, thoughts, or emotions. The Ideal Form is just another way of saying the spirit or soul. Only the immortal and unchangeable can be “Ideal” so this term can only reference the spiritual worlds, spiritual beings, and the spiritual faculties of man.