Deep sleep brings on a sense of non-dualistic peace with it. This experience one gets only in the absence of the ‘I’.+

The famous peace invocation of Isa Upanishad says: ~

Om Purna- madah, purna-midam purnat-purnam-udacyate Purnaysa purna-madaya purna-meva-vasisyate

This means: ~ All this is full /from fullness, fullness comes when fullness is taken from fullness/ fullness still remains.

The fulness of consciousness means- consciousness without the illusory division of form, time, and space.  The fullness of consciousness means Oneness. Oneness. Oneness is Advaita.  Advaita is the nature of the Soul, the Self, which is God in truth.  There is nothing that is not God in truth.

Sage Goudapada quotes from the Upanishads: ~ "There's no plurality here"; "The Soul through its powers appears to be many"; "those who are attached to the creation or production or origination go to utter darkness"; "the unborn is never reborn, for what can produce it?”. 

Chandogya Upanishad: ~   sarvam khalvidam brahma - all this (universe) is verily Brahman. By following back all of the relative appearances in the world, we eventually return to that from which it is all manifest – the non-dual reality.  

Deep sleep brings a sense of non-dualistic peace with it. This experience one gets only in the absence of the ‘I’. Therefore, there is a need to investigate what this ‘I’ is? The ‘I’ appears and disappears.

A deeper investigation reveals the fact that the ‘I’ is present in the form of the mind. The mind is in the form of the universe. The universe appears as waking or the dream (duality) and disappears as deep sleep (nonduality).

‘Self’ is not the ‘I’. If you hold the ‘Self’ as ‘I’ then you will never be able to realize the truth, which is beyond the form, time, and space. 

The ‘Self’ is the Soul, which is present in the form of consciousness. The Soul is the witness of the ‘I’ that appears and diapers. Thus, the ‘I’ is not permanent.

That is why Bhagavad Gita: ~ The permanent is always there, only the transient ‘I’ comes and goes. (2.18)

The ‘I’ hides the Soul, the Self, which is present in the form of consciousness. 

People think the ‘I’ without the body is the ‘Self’. The seeker has to understand the fact that ‘I’ is not the ‘Self’, but the witness of the ‘I’ is the true ‘Self’, which is eternal.

That is why Ashtavakra Gita 16:10: ~ If you desire liberation, but you still say 'I',  if you feel the ‘‘Self’’ is the ‘I’, you are not a wise man or a seeker. You are simply a man who suffers.

People are stuck with the reality of the ‘I’, which they take as real because some Gurus have propagated the ‘Self’ as the ‘I’. There is no need to convince such mindsets. The seeker of truth accepts only the truth nothing but the truth.: ~ Santthosh Kumaar