The only real existence is that of the one and only God, which is the Soul, the Self.+

The only real existence is that of the one and only God, which is the Soul, the Self.  Thus one has to reject all the ideas of god other than the Soul, the Self.

Rig Veda: ~ 'Prajnanam Brahma'- Consciousness is the ultimate reality or Brahman or God in truth.

Do not accept any other truth other than the consciousness. Consciousness is the ultimate truth,  Nothing is real but consciousness. Nothing Matters but realizing the ultimate truth. Consciousness is everywhere and in everything. Let these words be inscribed in your subconscious

Brahman— The One Without the  Second:

The Atman is self-evident (Svatah-Siddha). It is not established by extraneous proof. It is not possible to deny the Atman because It is the very essence of the one who denies It. The Atman is the basis of all kinds of knowledge, presuppositions, and proofs. Self is within, Self is without; Self is before, Self is behind; Self is on the right, Self is on the left; Self is above and Self is below. Brahman is not an object, as It is Adrisya, beyond the reach of the eyes. Hence the Upanishads declare: “Neti Neti—not this, not this....” This does not mean that Brahman is a negative concept, or a metaphysical abstraction, or a nonentity, or a void. It is not another. It is all-full, infinite, changeless, self-existent, self-delight, self-knowledge, and self-bliss. It is Svarupa, essence. It is the essence of the witness. It is the Seer (Drashta), Transcendent (Turiya), and Silent Witness (Sakshi).

Sage Sankara’s Supreme Brahman is impersonal, Nirguna (without Gunas or attributes), Nirakara (formless), Nirvisesha (without special characteristics), immutable, eternal, and Akarta (non-agent). It is above all needs and desires. It is always the Witnessing Subject. It can never become an object as It is beyond the reach of the senses. Brahman is non-dual, one without a second. It has no other besides it. It is destitute of difference, either external or internal. Brahman cannot be described because description implies a distinction. Brahman cannot be distinguished from any other than It. In Brahman, there is not distinction between  substance and attribute. Sat-Chit-Ananda constitutes, the very essence or Svarupa of Brahman and not just Its attributes. The Nirguna Brahman of Sage Sankara is impersonal.

If Sage Sankara’s wisdom is interpreted on the base of ego it creates a different meaning. If one learns to interpret on the base of the Soul, the Self then it takes him to realize the ultimate truth or Brahman or God in truth.

Sage Sankara said:~ Neither by the practice of yoga nor philosophy, nor by good works nor by learning, does liberation come, but only through the realization that Atman and Brahman are one in no other way. (1) VivekaChudamani v 56, pg 25

Advaita only means the negation of duality. The soul, which is present in the form of consciousness, is the ultimate truth or Brahman or God in truth. 

Consciousness is the cause of the origin, maintenance, and withdrawal of the universe is Advaita (i.e. non-dual), which means that consciousness transcends all conceptions, positive and negative. Nothing positive can ever be imagined or said about it.

Consciousness is existence absolute, awareness absolute.  Existence absolute means that consciousness is not unreal or non-existent. And it is not unconsciousness.  Nothing positive can be stated about consciousness.

Sage Sankara founded his Advaitic wisdom  either on reason independent of Sruti or on Sruti confirmed by reason."   Sri, Sankara's commentary on the Mandukya Upanishad, II, 1:  This [the unreality of duality] is borne out by the Srutis ... But it is possible also to show the unreality of the object world even from pure reasoning, and this second chapter is undertaken for that purpose.

Sage Sankara himself had often said that his philosophy was based on Sruti, or revealed scripture.  This may be because Sage Sankara addressed the ordinary man, who finds security in the idea of causality and thus in the idea of God—and Revelation is indispensable to prove the latter.  He believed that those of superior intelligence, have no need of this idea of divine causality, and can, therefore,  dispense with Sruti and arrive at the truth of Non-Dualism by pure reason. 

Sage Sankara gave out what was of most use to the greatest number of people. Therefore, in the commentaries on the Upanishads, such as the famous Mandukya, he gave the highest non-dual message of the identity of Atman and Brahman, revitalizing the philosophy and practice of Advaita, while in the commentaries on the Brahmasūtra he gave lesser teaching, positing both higher and lower Maya and higher and lower Brahman (Ishvara) to explain creation for those of lesser intellects until they were ready for the highest truth.

Only through Self-knowledge or Brahma Gnana or Atma Gnana negation of duality is possible. The Soul, the Self, which is present in the form of consciousness, is the ultimate truth or Brahman. Consciousness is the cause of the origin, maintenance, and withdrawal of the universe is Advaita (i.e. non-dual), which means that consciousness transcends all conceptions, positive and negative. Nothing positive can ever be imagined or said about it.  Consciousness is existence absolute, awareness absolute.  The existence of absolute means that consciousness is not unreal or non-existent. And it is not unconsciousness.  Nothing positive can be stated about consciousness.

The nature of the Soul, the Self is non-dualistic silence. Nondualistic silence is like a deep sleep state.  The silence indicates that the nature of the formless Soul, the Self is inexplicable, indescribable, and unimaginable.  The Soul, the Self is the one without a second. There is not the least shadow of multiplicity in the formless soul, which is present in the form of consciousness."

A   person, seeing a rope in dim light, mistakes it for a snake. He is as much frightened as he would have been if there had been a real snake there.  The snake is said to have an ‘illusory reality.  The illusory snake is described as a superimposition on the rope. The snake is not real, because, it is found on examination with a light that it never existed there. At the same time, it was experienced as reality till ignorance prevailed. Similarly, this waking experience is experienced as reality due to ignorance. When wisdom dawns then the unreal nature of the waking experience is exposed.  At the dawn of Self-knowledge or Brahma Gnana or Atma Gnana, the waking experience has no existence apart from consciousness. Consciousness is the ultimate truth or Brahman. The waking experience is therefore said to be superimposed on consciousness in the same way, as the dream is superimposed on consciousness.  The waking experience is   practical reality till attainment  of Self-realization.  Consciousness alone has absolute reality; because it is absolutely changeless because it is formless.      

Maya and Brahman, Jagat (world) and Ishvara (creator), Guru (teacher) and Shishya (disciple), the holy rituals, traditions, the three worlds, the three bodies, and so forth are the reality within the illusory duality.  This seeming duality is a hypothesis, not to establish duality, but to disprove it. Advaitic or non-dualistic truth has nothing to do with the illusory duality. The  Soul, the Self, which is present in the form of consciousness is the ultimate truth or Brahman. 

Consciousness is neither dual nor non-dual.  Some orthodox claim Atman is dual, some that Atman is non-dual; they do not know the ultimate truth. The Atman or soul is above duality and non-duality". 

The seeker has to realize the fact that, duality is a reality only from the standpoint of the waking entity or ego. One thinks that he is an individual separate from the world and that the world existed prior to him and he is born in it afterward. Till this conviction is there he will not be able to grasp the Advaitic or non-dualistic truth.

Sage Sankara ’says:- Gnana is common to all religions.  

There is nothing like One Gnana for a Hindu and another for a Christian.

The Advaitic wisdom of Sage Sankara can be summed up in the following statement:-

Brahma Satyam, jaganmithya, jivobrahmaivanaparah: - Brahman alone is real; the world is non-real,  and the individual Self is essentially not different from Brahman.

This is the quintessence of Sage Sankara’s Advaitic wisdom.:~Santthosh Kumaar