One has to know ‘What is mind? ‘What is the substance of the mind?’ and ‘What is the source of the mind?’ in order to realize the Non-dualistic or Advaitic truth.

When many candles are kindled from another, it is the same flame that burns in all candles; even so, the one Brahman appears to be many.

Gospel Thomas logian 22 :- Jesus saw infants being suckled.  He said to his disciples,  “These infants being suckled are like those who enter the kingdom.

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They said to him, “Shall we then, as children, enter the kingdom?”

Jesus said to them,  “When you make the two one, and when you make the inside like the outside  and the outside like the inside, and the above like the below, and when you make the male and the female one and the same, so that the male not be male nor the female is female; and when you fashion eyes in the place of an eye,  and a hand in place of a hand, and a foot in place of a foot, and a likeness in place of a likeness; then will you enter the kingdom.”

When one discriminates between the three states and the formless witness of the three states he will realize the universe is mere illusion.  Thus, it is necessary to understand the fact that, the formless witness is apart from the mind, which is present in the form of the universe and the universe appears as the waking or the dream.    The mind or universe was non-existent in deep sleep.  The witness of the coming and going of the three states is birthless and apart. This has to be grasped mentally   just as one knows a sound by its contrast to silence.

Self is not ‘you’ but the self is that witnesses ‘you and the world’ together without the physical apparatus. You are the false self (ego or waking entity) within the false experience (waking) bound by birth, life and death and form, time and space whereas the ‘Self ‘ is birthless and deathless because it is formless. Thus the self is not limited to waking state alone because it pervades everything and everywhere in all the three states. Thus limiting the ‘self’ to waking entity alone is the cause of the ignorance. 

The dream entity (you) and the dream world becomes falsehood when waking takes place. Similarly the waking entity (you) and the waking world become falsehood when wisdom dawns. Wisdom dawns when waking entity (you) realizes it itself is not the self but the self is that which witnesses the coming and going of the three states. The witness and the three states are one in essence. That essence is consciousness (Atman). 

Thus consciousness is ultimate truth or Brahman. Atman is second to none.  One has to know ‘What is mind? ‘What is the substance of the mind?’ and ‘What is the source of the mind?’ in order to realize the Non-dualistic or Advaitic truth.