Brih Upanishad: page 32. "Yoga does not yield truth or liberation."+

Sage Sankara says: ~ Yoga is not the means of liberation (page 132-133 - Commentary on Brihadaranyaka Upanishad.

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Yoga can yield only the duality because everything that one can do or practice becomes a vanishing 'known.' It yields relative truth based on imagination, which is true from the physical viewpoint, not the non-dualistic truth, which is the ultimate reality. 

Remember:~ 

Ashtavakra says: - "This is your bondage, that you practice Samadhi or meditation.”

Remaining thoughtless in the waking experience is yogic Samadhi. Yogic Samadhi is not the Advaitic wisdom 

Brih Upanishad: page 32. "Yoga does not yield truth or liberation."

One who is in Samadhi will not know that this universe as consciousness; therefore, yoga is not the means to Self-knowledge or Brahma Gnana or Atma Gnana.

In Samadhi the yogi knows nothing, sees no universe; so if there is nothing but blankness. The blankness is not the Advaitic wisdom. 

The yogi does not know the nature of the universe. If the universe is not seen in the Samadhi, then there is no need to use the word Atman and Brahman. The yogi is unaware of the Advaitic truth, which is hidden by ignorance.

By shutting his eyes in Samadhi, the yogi does not know the universe, which confronts him. Hence, the universe can't be known as the Soul or the consciousness through yoga. 

One is in a non-dual condition in deep sleep or Samadhi, One without a second, true, but he did not know it at the time. He says only in the waking experience afterward. Hence, there must be an inquiry so that you find non-duality whilst you are awake so that you can see nonduality at the time, not afterward. Hence, there is a need to inquire into the nature of the universe and know it as the Soul or the consciousness whilst one is awake and not during sleep or Samadhi.

Advaitic truth is the ultimate truth. Yogis, mystics, and religious teachers do not accept the path of wisdom because it pries into the truth, the source, and the validity of the knowledge they claim. Therefore, it is the most difficult part of the study of the Advaita.:~ Santthosh Kumaar