Here is a short definition of the soul, by Roberto Assagioli.
M.L. What is the relationship of the soul and the personality?
R.A. The difficulty in answering this question is first of all a semantic one, due to the very different meanings in which the two words have been and are being used. The American psychologist Allport has quoted about fifty definitions of the personality; I don’t know how many one could give of the soul! Therefore one should always define clearly the meaning in which one uses these words.
Let us consider the word soul. Keyserling and other modern writers use it to indicate the emotional nature or aspect of the personality. Jung’s definition of soul is “a definitely demarcated function – complex that is best characterized as a ‘personality'” (Psychological Types, p.508).
In the Christian usage, the word soul is used in a rather loose way. In some cases it connotes the immortal soul, made “in the image and likeness of God”, but in others, it corresponds more to the emotional nature, for instance, in the phrases “My soul is sad”, “My soul invokes God for help”, etc. Evidently, this is not the immortal soul but the emotional part of the personality.
I think your question refers to the relationship between the personality and the soul in the spiritual sense, that is, the spiritual Self (the Atman which is one with Brahman, both individual and universal).
This brings us back to the Ego and the Self, because the human personality is characterised by the possession of self-consciousness, or, in other words, the I or Ego is the core of the personality. Now the Ego should be regarded as a projection or a reflection of the spiritual Self. Therefore essentially it partakes of the nature of the spiritual Self, but it is so much veiled by “the 70,000 veils of maya”, that is, by its multiple identifications with all kinds of psychic contents (sensations, drives, emotions, thoughts, etc.) that it has lost all remembrance of its origin.
Thus we have the paradoxical situation of the personal self denying its “father”, its origin and source. It can also be called the paradox of duality and unity. This is the deep meaning of the old injunction: “Become what you are”. It could be expressed in modern terms as “Recognise your source, your origin, the spiritual Self, and unite in consciousness as much as possible with It until you achieve an increasing realisation of this identity, until it becomes permanent.” This is the drama of man’s existential situation, the meaning and purpose of human evolution.
(Dialogue with Roberto Assagioli. Discussion between: DR. Roberto Assagioli (R.A.), DR. Graham C. Taylor (G.C.F.), Martha Lazura Crampton (ML) May, 1966)
Read also the article: The Rebirth of the Soul.