Do not compare Sage Sankara's wisdom with dualistic Gurus wisdom or any other wisdom and even with the Advaitic orthodoxy,

No Guru after the 8th century propagated the Advaitic wisdom of Sage Sankara was hidden and was imparted only to a few.

Sage Sankara time in the 8th century, there was no Hinduism.

Santana Dharma or Vedic religion has no founders whereas Advaita and qualified Advaita and Dwaita are identified with their founders. All of them have non-Vedic rituals barred by the Vedas.

The dualism came only in the 12th century. The orthodox Advaita and Dvaita are adulterated add-ons. Both Advaita and Dvaita schools claim that they are based on the Vedas but they indulge in non-Vedic activities and they condemn each other with the Upanishads and Puranic citations and try to prove they are right and others are wrong.

The religion, including orthodox Advaita, is nothing to do with the ultimate truth or Brahman because they worship idols, human worship, and symbol worship and indulge in non-Vedic rituals barred by the Vedas.

In the 8th century, Sage Sankara solved the mystery of the universe and the mystery of God. 

Do not compare Sage  Sankara’s with dualistic Saints and Gurus wisdom or any other wisdom even with the Advaitic orthodoxy, which is also dualistic.

There are two kinds of audiences: ~

1. The ordinary ones who desire the transitory heaven and other pleasures obtained as a result of ritual sacrifices.

2. The most advanced seeker who seeks to know the truth, which is hidden by ignorance.   

The Advaitic orthodoxy is meant for the first audience, to help lead its followers along the way. The path of wisdom wits emphasis on the Advaitic wisdom is meant for those who wish to go beyond such transient pleasures.

Sage Sankara’s Advaitic wisdom is nothing to with religion and religious Gods and the scriptures.

Sage Sankara: ~VC- “Neither sacred baths nor any amount of charity nor even Hundreds of pranayamas* can give us the knowledge of our own Self. The firm conviction of the nature of the Self is seen to proceed from inquiry along the lines of the salutary advice of the wise.

Sage Sankara said:~ Talk as much philosophy as you like, worship as many Gods as you please, observe ceremonies, and sing devotional hymns, but liberation will never come, even after a hundred eons, without realizing the oneness.  

Upanishad says ~ “The human goal is to acquire Self-Knowledge and they indicate that belief in the personal Gods, yoga scriptures, worship, and rituals are not the means to Self –Knowledge, then why anyone should indulge in it. Religion, the concept of an individualized god, and scriptures are the greatest obstacle to realizing non-dual truth or Self-realization because they are based on a false Self. The seeker of truth has to search for the ultimate truth without losing himself in the labyrinths of philosophy, through deeper self-search and assimilating and realizing it.

That is why Sage Sankara says: ~ “One without knowledge does not obtain liberation even in a hundred births, no matter which religious faith he follows. (Bhaja Govindam)

Thus, the path of wisdom is the only means. Then it is no use going a roundabout way, trace the Brahman which is the formless substance and the witness of the universe (mind). By tracing the source of the mind or the universe, one will be able to realize the Brahman.

Yoga Vasistha says:~ Self-knowledge or knowledge of truth is not had by resorting to a Guru (preceptor) nor by the study of scripture, nor by good works: it is attained only by means of inquiry inspired by the company of wise (Gnani). One’s inner light alone is the means, naught else. When this inner light is kept alive, it is not affected by the darkness of inertia.

Sage Sankara himself has warned us not to use ambiguous words and to practice semantic analysis in his book "Definition of one's own Self. (Page 199, v.24 of "Sankara's Selected Works)

Sage Sankara: - Loud speech, the profusion of words, and skilfulness in expounding scriptures are merely for the enjoyment of the learned. They do not lead to liberation."

Perfectly tame your own self by knowing ‘what is the truth’ and ‘what is untruth to have a mental yardstick to discard the untruth. Sage Sankara the seeker must know what is truth and what is untruth.

Sage Goudpada: ~ To establish the truth of Non-duality by sheer reasoning alone. He begins by defining "What is real?" "What is unreal?" etc, because that is the right way to discuss or teach. People must first know what they are talking about. (Manduka Karika)

Sage Sankara says you must first know what is before you. If you cannot know that, what else can you know or understand? If you give up the external world in your inquiry, you cannot get the whole truth.

Swami Vivekananda: ~ “Oneness is the Secret of Everything”.

Nothing is needed for acquiring Self-knowledge or Brahma Gnana or Atma Gnana other than perfect understanding, assimilation, and realization of ‘what is what”

The dualistic illusion is present only when form, time, and space are present. The form, time, and space are one, in essence. The ego, body, and the world are one, in essence. 

Birth, life, death, and the world are one, in essence. The three states are one, in essence. That essence is consciousness. The thinker, thought and the world is one, in essence. Thus, there is no division in consciousness in reality.

The look of an object will depend upon the medium through which the observer views it. In fact, our mental and intellectual conditions determine the life observed and experienced. The commoner viewing the life will see differently from a Gnani viewing the same life. Each one interprets the life that they see in terms of their existing knowledge. The commoner sees everything based on the ego therefore the life he experiences as a reality, whereas a Gnani sees life is an illusion created out of consciousness and he is fully aware of the fact that, there is no second thing that exists other than the Soul, which is present in the form of consciousness (subject). Thus, all the objective observation is based on the false self, which has to be bifurcated to realize what I am saying. : ~ Santthosh Kumaar