Mentally reducing the dualistic illusion into nondualistic reality is Advaita.+

Consciousness is the ultimate truth. There is no higher truth other than consciousness.  To realize this truth, there is no need to follow any path. 

There is no need to follow anyone. There is no need to become a wandering monk. There is no need to renounce worldly life. Realizing consciousness (Spirit) is ultimate is spirituality.

There is nothing else to realize other than realizing there is no second thing that exists other than consciousness. Realizing the consciousness is second to none is truth- realization.

Even if you search for million years you will only come to a final conclusion and realization that the world in which you exist is nothing but consciousness.

If the world, in which you exist is nothing but the consciousness,  then what else is there to realize other than realizing the consciousness alone is real and the world in which you exist is merely an illusion.

 If the world in which you exist is merely an illusion the experience of the birth, life, and death that happens in the illusory world is bound to be an illusion.

If the world, in which you exist is an illusion then the division of the form, time, and space is merely an illusion because the Soul, the Self, is present in the form of consciousness.  The Soul, the  Self is the fullness of consciousness.  

Mentally reducing the world, in which you exist into consciousness leads to Self-awareness. Realizing the consciousness as the ultimate truth is Advaita. That is mentally reducing the dualistic illusion into a non-dualistic reality is Advaita.

Sage Sankara has declared Advaitic truth 1200 years back but it was hidden and imparted only to a few. Even scientists may declare in the future the world is nothing but the consciousness the Sage Sankara alone is qualified for the noble prize, not the scientists because Sage Sankara declared it 1200 years back. Sage Sankara’s Advaitic wisdom has been lost: people misinterpret and falsify. Advaita is not a theory but Advaita is the rational truth, the scientific truth, and the ultimate truth. But nobody knows it. The teachers of philosophy and the Gurus or religion do not want to inquire into truth and have no time for it.

Sage Sankara’s Advaitic wisdom is nothing to do with religion.  Thus, all his religious teaching which is meant for the ignorant populace has to be bifurcated from his wisdom. 
Remember:~ 

India is the ancient land, where wisdom made its home India whose soil has been trodden by the feet of the greatest sages of truth like Bhagavan Buddha, Sage  Sankara, and Sage Goudpada.

India is the fountainhead of Advaitic wisdom. Advaitic wisdom is brighter, greater which unfolds the mystery of the universe, which contains the whole of humanity.

The goal of the truth-seeker is to acquire Self- knowledge or Brahma Gnana or Atma Gnana. Self-knowledge or Brahma Gnana or Atma Gnana is inherent in every seeker of truth. Self-knowledge or Brahma Gnana or Atma Gnana does not come from outside, it is hidden within the world in which we exist.

Self-knowledge cannot be attained by the study of the scriptures and intellectual understanding or by bookish knowledge. Therefore, there is no use in studying the scriptures and philosophy to acquire non-dualistic wisdom. That is why Bhagavan Buddha rejected the scriptures, and even Sage Sankara indicated that the ultimate truth lies beyond religion, the concept of God, and scriptures.

Bhagavan Buddha gave up yoga after practicing it for six years. He saw it could not yield truth.

Bhagavan Buddha gave up his austerities of yoga as impossible and useless.

Thus, Bhagavan Buddha got enlightenment only after he gave up Yoga. (Page.70/71 "Buddhism In Translation” by Warren)

Unless one exercise his Buddhi--reason--there is no chance of getting the ultimate truth or Brahman

Buddhism has not proved the truth of Nonduality. Buddha pointed out the unreality of the world, we agree. He told people they were foolish to cling to it. However, he stopped there. He came nearest to Advaita in speech but not to Advaita fully.

Dalai Lama said: Buddhism need not be the best religion though it is most scientific and religion and inquisitive. But Buddhism has no answer to certain questions like the existence of Atama [Soul] and rebirth. Dali Lama said that as an individual he believes in rebirth as he had come across a few cases of rebirth. Modern science, Dalai Lama hoped would unearth the mystery behind the rebirth. (In DH –dec-212009-Gulbarga).

Only when we independently search the truth without religion and its doctrine then we will be able to realize the truth beyond form, time, and space.

Bhagavan Buddha: ~ "It is better to conquer yourself than to win a thousand battles. Then the victory is yours. It cannot be taken from you, not by angels or by demons, heaven or hell."
Remember:~ 

Buddhists do not believe in God, they believe in emptiness First tell them that Buddhists don't believe in God, and secondly, you tell them they believe in emptiness. That's worse! That they believe in "nothingness!" That's worse!

That's why you need to explain. Because when Buddhists say they do not believe in God, it does not mean that Buddhists don't believe in the nature of God! Because the nature of God is the nature of truth, is the Shunyata, or emptiness. The same! But Buddhists do not believe in the concept of God. Because in many ways you, you see, however, good the concepts are, it does not do justice for the Absolute. All the concepts of God will not describe, really, what God is.

Do you know what I'm saying? There is a wonderful saying by a great Buddhist master called Shantideva, who is a very great compassion master. He said, "Absolute is beyond the mind." That which is within the realm of mind is called the relative. "Absolute is beyond the mind." Since God is beyond the mind, it is beyond concept. Therefore empty, empty means free, open, like the sky. It doesn't mean emptiness in a nihilistic sense like my cup is empty of tea or something. (OSHO)

The point of the Bhagvan Buddha is that if God is non-existent, the entire creation including the ‘Self’ is non-existent. Sage Sankara wanted to establish the existence of the Brahman. For this purpose, He made the Atman as the Brahman. He brought out the identity of the ‘Self’ with the consciousness and made the Atman the Brahman. Since one will not negate the existence of the Self, he will accept the existence of the Brahman, which is the Atman or Soul, the innermost Self. Both Bhagavan Buddha and Sage  Sankara kept silent about the absolute unimaginable God. The same philosophy was dealt with by them from different angles in different situations.

Sage Sankara opposed the Buddhists only, who misunderstood Bhagavan Buddha and became atheists. 

According to Sage Sankara meditation always means the critical analysis about the Self to get salvation from worldly tensions. Due to the eccentric ego of the then atheists, Sage Sankara did not go beyond this since the atheists will not accept God beyond themselves. This limitation is not due to limited knowledge of Sage Sankara but is due to the then-existing situation of the psychology of the surrounding society. Even Bhagavan Buddha kept silent about God because the society dealt by Him consisted of Purvamimamsakas, who were strong atheists. 

Bhagavan Buddha told that everything including the Self is only relatively real (Sunya). This is correct because the Self is a part of the universe, which is relatively real with respect to the absolute unimaginable God. Bhagavan Buddha stopped at this point because the atheists cannot realize the existence of the unimaginable God indicated through His silence. : ~ Santthosh Kumaar