The mind cannot be purified because the mind itself is an illusion.+

Upanishads:~ Fools dwelling in darkness, but thinking they wise and erudite, go round and round, by various tortuous paths, like the blind led by the blind. ( Fools dwelling in darkness, but thinking they wise and erudite, go round and round, by various tortuous paths, like the blind led by the blind. (Upanishads Nikilanada - Ch II-5 P-14)

The mind cannot be purified because the mind itself is an illusion. Till one thinks the mind is within the body, he will not be able to acquire Self-knowledge or Brahma Gnana or Atma Gnana, because the body and the world are within the mind. And the mind is within the Soul.

Ignorance is the cause of the duality. The duality is the cause of the illusion (Maya).The Illusion is the cause of experiencing birth, life, death, and the world as a reality.

Self-knowledge leads to Self-awareness. The quest for truth is not the quest for acquiring the dualistic truth within the world. The seeker must have an intense urge to realize the truth which is beyond the form, time, and space.

The dualistic knowledge hides the truth beyond form, time, and space. The practical life within the practical world is nothing to do with the ultimate truth or Brahman.

The dualistic knowledge within the dualistic illusion is not Self-knowledge or Brahma Gnana or Atma Gnana.

This vast cosmos with all its contents (atom, molecule, sun, moon, planet, and star) all are created out of single stuff. That single stuff is the Soul, which is present in the form of consciousness. Knowledge of the single stuff is Self-knowledge or Brahma Gnana or Atma Gnana.

The Soul is the Self. the Soul is present in the form of consciousness. Awareness is the nature of the Soul or the consciousness. Consciousness is existence itself.

Consciousness is ever-present. Without consciousness, the world, in which you exist ceases to exist. Consciousness is Self-evident. It is not established by extraneous proofs. It is not possible to deny consciousness because it is the very essence of the one who denies it. Consciousness is the basis of all kinds of knowledge, presuppositions, and proofs. Consciousness is everything. Thus, consciousness is the ultimate truth or Brahman or God in truth.

Remember:~

Avadhuta Gita: ~ “The Atman cannot be purified through the practice of the six limbs of yoga, or through the annihilation of the mind, or through the instruction of a teacher. The Atman is the Reality Itself and It is Purity itself."

From the standpoint of the Soul, the ‘Self’, the visions, and Samadhi belong to the illusion because they are based on the false ‘Self’ (ego) within the false experience (waking).

It is not possible to stop thought for more than a half-second whilst in the waking state. If one succeeds in controlling thought and then banishes it, one passes into Nirvikalpa Samadhi, which is identical to deep sleep. The only difference between ordinary deep sleep and Samadhi, therefore, is that the ordinary man falls asleep involuntarily whereas the yogi has the satisfaction of knowing that he has passed into sleep by his own effort of will in banishing thoughts.

Yogic Sage Patanjali warns against sleep as a hindrance to yoga, he means when it occurs in the early stages of the practice before one has obtained the power of control and consequently to banish the thoughts. The fact that Samadhi is deep sleep is kept secret because people would not be tempted to take up yoga.

Yoga sharpens the ego, to enable it to keep away all extraneous thoughts when one gets out to reason in the practice of the next higher stage, i.e. Gnana. Yoga is thus simply a sharpening stone for the ego to enable it to take up Advaitic Gnana.

In Sutra Bashya and Mundaka: ~ Samadhi and sleep are identical. Brihad Upanishad does not advocate Samadhi.: ~Santthosh Kumaar