"The Gods themselves are Facets of the Soul requiring attention."(Marcilio-Ficino).
Esoteric philosophy reconciles all religions.
There is no scientific evidence of its existence. We can only rely on the information from the fore-runners of the human race such as : Adepts, Masters of Yoga, Saints and Mystics. Ancient sacred texts which in turn were handed down orally from generation to generation before being committed to writing are often referred to, and as they are attributed to Avatars such as Patanjali, Krishna and more recently Jesus who mentions the "soul" from time to time in the gospels. The best books that I have encountered on this subject are " The Soul, A Compilation" based on A.Bailey writings, and that remarkable tome 'The Treatise on Cosmic Fire".The Soul is an unknown, and has to be accepted on faith or intuitive knowledge. Only that information from those with direct experience is available and language has proved lacking for this purpose.
The Universal Soul or Anima Mundi is a direct emanation of the Manifesting Trinity. A metaphysical definition, for what it is worth is "A Vortex of Twelve Energies held together by the Will of the Monad". Another is, "The Result of The Relation between Spirit and Matter", also "A Mediator and Middle Principal between the Manifest and the Unmanifest". It has many names :"The Christ Principle", "The Form Building Aspect", and "The Essence of Individuality". It appears that a list of the properties and functions of "Soul" is the nearest we can come to understanding It .The Universal Soul represents The Force of Evolution and is the 2nd. Aspect,'The Son". It is "Unified Sentiency" of which the Human Soul is a part, and That Force which is Impersonal Love propelling all lifestreams back to their Source through Karmic Experience. It developed the human form over millions of years to form a link between the Upper and Lower Triads. At the same time it is also an Instrument of Law by way of the use of Manas(mind). As the Principle of Intelligent Activity it is more under the influence of The Feminine Aspect of The Logos, giving rise to the many names of The Goddess throughout history. In the constitution of the human unit it is synonymous with the Higher Self, and source of the Faculty of Intuition. It is not generally aware of the personality, but is conscious of, and active within its own groupon the buddhic plane. Until stimulated by unselfish action and spiritual exercise it is not normally aware of the lower self. It can be completely disassociated and sever its connection in cases of prolonged and extreme depravity, and less permanently in obsessive materialism.
A future phase of evolution will be "Soul Consciousness" and is the inevitable goal for all humanity, and beyond that is "Ascension "(which by the way, is not that which is loosely mentioned in some New Age literature and is the Final Initiation terminating terrestrial existence). Some will take advantage of shortcuts to this end, using the various methods which have been made available. The metaphysics of this process involves the raising of the Kundalini Power which is described in the pages on Yoga Philosophy. It is through the etheric body and its vortices of psychic energy that Soul Contact is to be made.
The Soul is sometimes called the "The Solar Angel"and "The Angel of The Presence", there are many other names given to this most mysterious part of the human unit. In order to function in the cosmos the Soul creates a suitable vehicle called the "Causal Body". During the intervals between incarnations the lifestream may spend many years on the Plane of the Soul (The Buddhic Plane), depending on Karmic Factors and the associated Ray of The Monad. The Causal Body is virtually immortal in our conception of time, ultimately it is left in favour of a "Spirit Body"on the realm of" Monadic Consciousness" which seems to be way beyond the stage of the Adepts. These "bodies" are entirely unlike our notion of what a body is like. They are pure energy egg-shaped and free to move with speed of thought and can take on form of any kind. The 3rd.Eye, is the "Eye of The Soul", dormant in man until some degree of soul awareness is present and tangible. It is "The Eye of Shiva", the organ of clairvoyance and the exercise of magical powers.
In the Hindu pantheon Indra is Lord of the Buddhic plane, the Home of the Soul, the symbol of which is that of Air (Aquarius ), just as Agni is Lord of the Mental plane, Fire and Kundalini.