Buddha, Sri, Sankara and Sri, Goudpada have declared non-dual truth centuries back but one has to reach the destination with scientific or rational investigation not through punditry and intellectuality

The Buddha taught that believing in gods and religion and yoga  was not useful for those seeking to realize enlightenment. that is why  Buddha declared:-

Believe nothing because a wise man said it,
Believe nothing because it is genera lly held.
Believe nothing because it is written.
Believe nothing because it is said to be divine.
Believe nothing because someone else said it.
But believe only what you yourself judge to be true.
-Buddha
(from The Mystic Vision
Compiled by Andrew Harvey and Anne Baring)

Even Swami Vivekananda said: - “You have to grow from the inside out. None can teach you, none can make you spiritual. There is no other teacher but your own soul.”

For the same reason Raman Maharishi said:  fortunate are the one who do not lose themselves in the labyrinths of philosophy. Bhagwan says: Take Vedanta, for instance: it speaks of 15 pranas the names and functions of it   which the student is asked to commit memory. Will it not be sufficient if he thought, only one prana does the whole work of maintaining the body? Again the antakaran is said to think, to desire, to will, to reason etc. Why all these details? Has anyone seen antakarana, or all these pranas? Do they really exist? They are conceptual divisions invented by teachers of philosophy by their excessive analysis. Where do all these concepts end? Why should confusion created and then explained away? Fortunate is the man who does not lose himself in the labyrinths of philosophy, but goes straight to the source from which they all arise. (GURU RAMANA .By S.S Cohen -vii Danger of philosophy-Page -58-59)

Religions are based   on the beliefs of Gods and dogmas. However, in pursuit of truth, merely believing in doctrines is beside the point. Seeker of truth   should not accept doctrines just because he read them in scriptures or are taught them by priests/gurus/god -men.

Swami Vivekananda said:-THE MASSES IN INDIA CRY TO SIXTY MILLION GODS, AND STILL DIE LIKE DOGS. WHERE ARE THESE GODS? - Swami Vivekananda  (Delivered In San Francisco, on May 28, 1900)

Instead of studying the doctrines to be memorized and believed, one has to learn how he can realize truth for himself without the doctrines. The focus of the truth seeker is on truth rather than blind belief. 

A religious guru or yogi is too enthusiastic to have everyone as his disciple, and he will push himself on others with his advices, authoritative scriptural knowledge. Religious guru or yogi wants to keep everyone in the domain of religion and yoga. 

Brihad Aranyaka Upanishad/ 3/8/9: It is in truth that Imperishable, O Gargi, who is not seen but is the seer, who is not heard but is the hearer, who is not thought but is the thinker, who is not known but is the knower. There is no other seer but him, no other hearer but him, no other thinker but him, no other knower but him. And it is that Imperishable which is the warp and the woof of space.”

Thus, the Vedic scriptures recognize the unity of REALITY without any human intervention or intercession.

Religion and mysticism is a species of mesmerism affecting weaker or impressionable minds. Thus the panoply of a guru’s religious robes or presence of god men creates unconscious suggestion in weaker minds of a superior power or magical knowledge. Similarly, mass visitors to ashrams are suggested into thinking they experience great peace and their wishes will be fulfilled if they unconditionally surrender to guru or god men.  Since they are unconsciously hypnotized into believing that will happen. However, when a strong mind which is aware of the truth meets a guru or god men are entirely unaffected.  Whatever happening within the waking experience is part of the duality, thus it cannot be part of the reality.

 

Even in the Buddhism: - Buddhist teaching has itself become a kind of interactive and self-evolving process, much like its idea of pratityasamutpada. However, the end goal is still Nirvana, which is an experience ultimately beyond all concepts and language, even beyond the Buddhist teachings. In the end even the attachment to the Dharma, the Buddhist teaching, must be dropped like all other attachments. The tradition compares the teaching to a raft upon which one crosses a swift river to get to the other side; once one is on the far shore; there is no longer any need to carry the raft. The far shore is Nirvana, and it is also said that when one arrives, one can see quite clearly that there was never any river at all.

Most of the dualistic sages approach was more practical, and they stuck with the reality of the world, they took it as real.  Whereas 

 Sri, Sankara says: one must first know what is before him. If he cannot know that, what else can he know or understand? If he gives up the external world in his inquiry, he cannot get the whole truth.

Sri, Sankara says in VC-63. Without causing the objective universe to vanish and without knowing the truth of the Self, how is one to achieve Liberation by the mere utterance of the word Brahman? — It would result merely in an effort of speech.

The scriptures and theories and teaching based on the ego are not the yardstick. Using them as yardstick to understand and assimilate the truth will lead one towards pursuit of arguments. Seeker of truth has to discover on his own, the truth of his true existence by inquiring “what is mind?” and “what is substance of the mind?” and move forward.  

The ultimate truth is one without the second, the one is not in the sense half or two, but the one that remain forever One, without the second.  The consciousness is all pervading. There is no place where consciousness is not.

Consciousness is in everyone, consciousness is in everything .consciousness is one behind many. Consciousness alone is. It means the universe is the visible form of consciousness.

More than he wants to help people, he wants to help his ego. A serious seeker of truth will he  only uses people and impose his inherited idea of religion and god on them, usually unintentionally because he himself is more unconscious than others of the ultimate truth.

A Gnani is not enthusiastic to have anyone as his disciple. He never identifies himself as Gnani.  He does not impose his ideas on anyone. However, he identifies the serious seeker and guides them as a fellow seeker. It is very difficult to identify a Gnani, because he never claims himself to be guru or teacher.

Most people are not aware what really they are seeking. They start there pursuit with their inherited religious ideas and as they go deeper they will feel that religion and yoga are inadequate to quench their thirst.

A serious seeker will realize the fact that, he is looking for something else, and he is now sure it is not self-assurance, fulfillment of dreams, fulfillment of social demands.   He will realize the fact that religion and yoga are means to quench his inner thirst. 

A Gnani dearly cares about the serious seeker but will stay aloof, he knows that if seeker needs to be assisted by him, he will approach or rather be drawn to approach him. He has no self-interest whatsoever and so anyone considered equally, for his love as anybody else, who ever comes, comes and if no one comes it is also fine.

Buddha, Sri, Sankara and Sri, Goudpada have declared non-dual truth centuries back but one has to reach the destination with scientific  or rational  investigation not through punditry and intellectuality. One has to mentally reach the final conclusion, than only the conviction becomes firm. Without the firm conviction the wisdom will not dawn. Therefore, there is a need to know consciousness is real all else is myth, which Sri, Sankara declared as the world is myth Brahman alone is real.
 

Sri, Sankara says Atman is Brahman and everything is Brahman is scientific declaration not religious or yogic. Sri, Sankara and Goudpada are more scientific than anyone else in the world. Since, the real Advaitic essence is hidden it cannot be got without the inner (mental)journey.

 

Goudpada says that:- The merciful Veda teaches karma and Upasana to people of lower and middling intellect, while Jnana is taught to those of higher intellect.

Gnana here is knowledge un-contradictable truth or scientific truth. Thus their scientific truth of the whole not part is declared by Sri,Sankara 1400 years back and thought only to those of higher intellect. Thus karma and upasana, yoga and orthodoxy has to be bifurcated in order to realize the ultimate truth or Brahman.  
 

Wisdom is for those are capable of inquiring into their own existence to know and realize the ultimate truth or Brahman.