The Kosha theory belongs to yoga. Yoga is not spirituality because the yoga is based on the body whereas the spirituality based on the Soul, the Spirit.*****

A Kosha usually rendered "sheath", is a covering of the Atman, or Self according to Vedantic philosophy. There are five Koshas, and they are often visualized as the layers of an onion.

1. Annamaya Kosha 
2. Pranamaya Kosha 
3. Manomaya Kosha –
4. Vijnanamaya Kosha
5. Anandamaya Kosha 

The Kosha theory is related to yoga. Yoga is not spirituality because the yoga is based on the body whereas the spirituality based on the Soul, the Spirit. 

All the Koshas are mere imagined theory based on the ego, which is the false self, within the false experience. Because everyone thinks the mind is within the body, whereas the body is within the mind, which is in the form of the universe.

 If the mind is there then only the universe is there.  If the universe is there then only the all its contents are there. Absence of mind is absent of the universe and its contents. Absent of the universe is absent from the individual experience of birth, life, and death.  The universe appears as waking or dream and disappears as deep sleep. The formless witness of the appearance of waking and dream is consciousness, which is the true self.
  

 On the base of consciousness as self, the universe or mind is merely an illusion.  The formless witness itself is the substance of the mind. Thus the mind or the universe and the Soul, the Self, which is present in the form of consciousness, are one in essence because the mind, which is in the form of the universe erupted out of the formless Soul or consciousness.  Thus everything within the mind or the universe is created out of consciousness. Thus everything is consciousness. Therefore, there is no scope for second thing other than consciousness because the body and the universe are also consciousness. Therefore the universe, which is in the form of mind, is a mere mirage created out of consciousness.  

 Therefore, KoshaS are mere divisions imagined and assumed because, when the self is not the body (form) but the Self is consciousness (formless)   there is no scope for the division.  Only when one thinks the physical body as self then only there is scope for division within the consciousness.

One has to stay totally in the awareness of the soul, which is in the form of consciousness within the waking experience. The world, the body, relationships – all are external to the true self /soul, which is consciousness. 

Thus all these scriptural theories hold no water when one becomes aware of the fact that the body is not the self. Thus all the theories based on the body as self-hold no water. 

When the Vedas and Upanishad declare that Consciousness or Atman is actually nothing but Brahman, then why go round and round, by various tortuous paths, like the blind led by the blind. One has to realize the fact that, the mind is in the form of the universe.  Trace the source of mind and realize that the source is consciousness. The mind arises from consciousness as waking or dream and subsides as deep sleep.   

In Mandukya Upanishad Brahman and Atman are defined as same:~

सर्वं ह्येतद् ब्रह्मायमात्मा ब्रह्म सोयमात्मा चतुष्पात् / sarvam hyetad brahmaayamaatmaa brahm soyamaatmaa chatushpaat – 

Mandukya Upanishad, verse-2

Translation:

sarvam(सर्वम्)- Whole/All/Everything; hi(हि)- Really/Just/Surely/Indeed; etad(एतद्)- This here/This; brahm(ब्रह्म)- Brahm/Brahman; ayam(अयम्)- This/Here; aatmaa(आत्मा)- Atma/Atman; sah(सः)- He; ayam(अयम्)- This/Here; chatus(चतुस्)- Four/Quadruple; paat(पात्)- Step/Foot/Quarter

Fragmented Verse:-

सर्वम् हि एतद् ब्रह्म अयम् आत्मा ब्रह्म सः अयम् आत्मा चतुस पात् / sarvam hi etad brahm ayama aatmaa brahm sah ayam aatmaa chatus paat

Simple Meaning:~

All indeed is this Brahman; This Atman is Brahman; He, this Atman has four steps/quarters.

While Brahman lies behind the sum total of the objective universe, some human minds boggle at any attempt to explain it with only the tools provided by reason. Brahman is beyond the senses, beyond the mind, beyond intelligence, beyond imagination. Indeed, the highest idea is that Brahman is beyond both existence and non-existence, transcending and including time, causation and space, and thus can never be known in the same material sense as one traditionally 'understands' a given concept or object.

Imagine a person who is blind from birth and has not seen anything. Is it possible for us to explain to him the meaning of the color red? Is any amount of thinking or reasoning on his part ever going to make him understand the sensation of the color red? In a similar fashion, the idea of Brahman cannot be explained or understood through material reasoning or any form of human communication. Brahman is like the color red; those who can sense it cannot explain or argue with those who have never sensed it.

Bhagavad Gita:~ brahmano hi pratisthaham -Brahman is considered the all-pervading consciousness which is the basis of all the animate and inanimate entities and material. (14.27)

In Advaita Vedanta:~ Brahman is without attributes and strictly impersonal. It can be best described as infinite Being, infinite Consciousness and infinite Bliss. It is pure knowledge itself, similar to a source of infinite radiance. Since the Advaitins regard Brahman to be the Ultimate Truth, so in comparison to Brahman, every other thing, including the material world, its distinctness, the individuality of the living creatures and even Ishvara (the Supreme Lord) itself are all untrue. Brahman is the effulgent cause of everything that exists and can possibly exist. Since it is beyond human comprehension, it is without any attributes, for assigning attributes to it would be distorting the true nature of Brahman. Orthodox Advaitins believe in the existence of both Saguna Brahman and Nirguna Brahman; however, they consider Nirguna Brahman to be the absolute supreme truth. 

Chandogya Upanishad:~One who meditates upon and realizes the self discovers that everything in the cosmos-- energy and space, fire and water, name and form, birth and death, mind and will, word and deed, mantram and meditation--all come from the Self.

So, it clearly says the one who meditates upon the self [consciousness] discovers that everything in the cosmos-- energy and space, fire and water, name and form, birth and death, mind and will, word and deed, mantram and meditation--all come from the Self. Therefore, there is a need to know the fact that, the true self is not physical but the soul in order to realize the fact that :  the cosmos-- energy and space, fire and water, name and form, birth and death, mind and will, word and deed, mantram and meditation--all come from the Self, which is in the form of consciousness. 

Ataman is Brahman. Brahman /Christ/the Absolute is alone real; this waking is unreal, and the three states are non-different from Brahman/God. 

Whatever is, is Brahman/Christ. Brahman/God itself is absolutely homogeneous. All difference and plurality are illusory."  Brahman/God is not a person, as the Absolute is not this. But if one wants to call it God/Paramataman, then fine. But it is not a person. Personifying it can make it easier to understand.:~Santthosh Kumaar