The "traditional" or established esoteric idea is that the soul or consciousness ascends through the different cosmic levels, finally returning to Godhead or Source. We find this idea in the early Upanishads, including the Taittiriya Upanishad (but not in Advaita Vedanta), in the Hermetica and the Xenocrates-Plutarch metaphysic, in Kabbalah, and even in more recent systems of thought like the Baha'i religion and Spiritualism.
As an alternative there was the idea of reincarnation. Rather than ascending "vertically" and returning after death to the Source, the soul or consciousness moves "horizontally" into a new physical body. This was an idea very popular not only in India (Hinduism, Buddhism, Jainism), but also the Greek and Hellenistic world (Orphism, Pythagoreanism, Platonism, Neoplatonism, Manichaeism, some forms of Hermeticism and Gnosticism), and among some Shamanic peoples: e.g. the Eskimos (Innuit) and certain tribes of Australian Aborigines
The Theosophists suggested a third alternative; a synthesis of the two. There is both the post mortem ascent back to the Higher Self, and also the process of reincarnation. But since the Personality is mortal, the only principle which can reincarnate in toto is the Higher Self. So we have:
Higher Self ---------Reincarnates)----->
| Second Death
Personality | post-mortem ascent through
(Mortal) | the "Intermediate World"
Body physical death
The Higher Self or Divine Soul when it starts out is just a Spark; it is still embryonic and nascent. It contains the potentiality of what it can become, but it has yet to actualise that. It is just like the transcendent Godhead, the Shiva-Shakti, which contained the potentials of all states of existence before creating/becoming those states of existence.
So to begin with the Divine Soul was a little spark, a little baby so to speak. Through its experiences in innumerable incarnations in psycho-physical nature, the Divine Soul developed and unfolded its own characteristics. Every Divine Soul had its own unique combination of experiences, and thus every Divine Soul became a unique being. So every Soul is different.
Every Soul is different. Just think about those words. It must be obvious to everyone with any sensitivity that the essence of each being - whether man or woman or dog or cat or tree or insect or protozoan - is unique. Every being has its own unique essence and personality, and of course this becomes more unique the further up the evolutionary scale one goes; i.e. the further the purusha-Soul evolves.
So, every human Divine Soul is different, and that means that every person has their own unique spiritual path to follow. Here of course we see the idiocy of the established exoteric and literalist religions, which arrogantly claim that you have to do it their way.
Through countless incarnations and experiences, the Divine Soul develops what could be called the "causal body". This is the "subtle body" that the Divine Soul carries with it from lifetime to lifetime, to serve as a kind of matrix or mould for creating physical and other bodies it needs.
So what we have therefore is a three-fold reality.
First there is the Divine principle, the Divine Soul or Higher Self itself, as the essential Presence within Matter. This is the "Higher Self" within every evolving being.
Then there is the Causal body, the linga or "mark" to use the Samkhyan term, the essential creative matrix, which, like the Divine Soul, is immortal and evolving.
Finally, there are the outer or manifest bodies, both gross (physical) and subtle (supraphysical). So in man/woman we can speak of - to use Theosophical terminology - an etheric body, an astral body, mental body, and so on. These outer or manifest bodies constitute the individual person.
Now, there is a constant feedback and interaction between these different principles and levels. The various manifest bodies are all constantly reacting with each other and with their physical, vital, mental, and psychic environment.
The Causal body originally creates the manifest bodies, and in turn receives impressions from them, but this interaction is not as great as the feedback between the various manifest bodies themselves.
Finally, the Divine Soul or Higher Self is in-fluenced by the manifest bodies, and in turn exerts an influence on them. This influence is very very slight in the case of a "young" Soul, but correspondingly greater as the Soul becomes more evolved.
Since the mundane personality and the Divine Soul are two distinct personalities, the question arises: can either exist in the physical body without the other?
Well, in normal circumstances it is highly unlikely that the Divine Soul or Higher Self can operate physically without the natural soul; even Adepts and Realised beings still maintained those psychological functions necessary for physical existence. Perhaps there may be a state in which the Higher Self can operate directly in the body without the mediation of the mental and the emotional natures, Mirra hints of such a thing.
As far as the mundane personality goes though, the answer is a quite definite Yes. For although a human without a Higher Self would be somewhat diminished, and lacking in that subtle intuitive something one could call "spiritual light", he or she would still continue to function pretty much as before. For the natural self is the normal state of the personality anyway; it is only exceptional spiritual beings who are able to function constantly from the Higher Self level. For the rest of us, the Higher Self comes and goes in consciousness like a fleeting yet beautiful source of inspiration; an uplifting, a widening, a larger, more selfless, more spiritual, more knowing awareness. And for some these moments are very rare indeed, and the con-sciousness very rarely moves out of its dull everyday material- and self-centred functioning and experiencing.