Advaita encompasses everything. Since Advaita requires heavy-duty intellectualism, it had to be progressively simplified.+

First Mundaka - Chapter 2 (8) - Fools, dwelling in darkness, but wise in their own conceit and puffed up with vain scholarship, wander about, being afflicted by many ills, like blind men led by the blind.

The ultimate truth or Brahman is beyond all philosophy. When the seeker realizes all his accumulation of knowledge from different sources is inadequate and useless in quenching his spiritual thirst, he will start his inner (mental) journey on his own. 

The journey is full of obstacles because the seeker has to drop all the accumulated dross and all the conditioning (samskaras) to cross the ocean of duality or samsara.

One could have all books and doctrines, spiritual schools, and different Eastern and Western Gurus; but no actual help for higher truth. 

One cannot realize the truth by reading books. The truth can never be described in words. for it cannot be written because the truth is nondual.  

That is why 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) Vivekachoodamani v 56, pg~25

As one indulges in deeper Self-search he will know somewhere he is going wrong, and it is for him to overcome the entire obstacle on his own by knowing what is obstructing his realization. 

The greatest hindrance is mixing religion, God, scriptures, yogic theories and intellectual speculations, and logical conclusions. Moreover, attachment to scriptures, personal God, and religious code of conduct keep one permanently in the grip of duality.

Scriptures are not needed in pursuit of truth. Even the Upanishads and the Sages of truth declare the same.

The ultimate truth has to be ascertained without the scriptures by realizing the Self is neither the waking entity not the dream entity but the Self is a formless Soul which is present in the form of consciousness. 

In the realm of truth form, time, and space are created out of single stuff. That single stuff is consciousness. 

Realizing the single stuff as the ultimate truth is Self-realization or truth realization. To realize this truth there is no need for the scriptures.

The ultimate truth has to be realized first then only it is possible to know what the scriptures are saying.

Scriptures are being added from time to time. This process will go on. There is the final authority among them? One contradicts the other: duality reigns supreme.

I quote Scriptural citations only after verifying reality and proving the truth, to point out that the scriptures teach the same thing. If one quotes them before having demonstrated the truth, then it is scholasticism.

Self-knowledge cannot be attained by taking sanyasa, by the study of the scriptures and intellectual understanding, or by bookish knowledge. Therefore there is no use in studying the scriptures and other scriptures to acquire non-dual 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 the scriptures.

There is only one Reality to be known, the same for all seekers, but the ways to it, are hidden by religion. Self-discovery is the only way, towards the non-dual Absolute without any religious doctrines, which will help the seekers to unfold the mystery of the illusion in which we all are searching for the truth of our true existence.

That is why Sage Sankara says: ~ VC 56. Neither by Yoga, nor by Sankhya, nor by good work, nor by learning, but by the realization of one's identity with Brahman is Liberation possible, and by no other means.

58. Loud speech consisting of a shower of words, the skill in expounding the Scriptures, and likewise erudition - these merely bring on a little personal enjoyment to the scholar but are no good for Liberation.

59. The study of the Scriptures is useless so long as the highest Truth is unknown, and it is equally useless when the highest Truth has already been known.

60. The Scriptures consisting of many words are a dense forest that merely causes the mind to ramble. Hence men of wisdom should earnestly set about knowing the true nature of the Self.

61. For one who has been bitten by the serpent of Ignorance, the only remedy is the knowledge of Brahman. Of what avail are the Vedas and (other) Scriptures, Mantras (sacred formulae), and medicines to such a one?

62. A disease does not leave off if one simply utters the name of the medicine, without taking it; (similarly) without direct realization one cannot be liberated by the mere utterance of the word Brahman.

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.

64. Without killing one’s enemies, and possessing oneself of the splendor of the entire surrounding region, one cannot claim to be an emperor by merely saying, ‘I am an emperor’.

65. As a treasure hidden underground requires (for its extraction) competent instruction, excavation, the removal of stones and other such things lying above it, and (finally) grasping, but never comes out by being (merely) called out by name, so the transparent Truth of the Self, which is hidden by Maya and its effects, is to be attained through the instructions of a knower of Brahman, followed by reflection, meditation and so forth, but not through perverted arguments.

66. Therefore the wise should, as in the case of disease and the like, personally strive by all the means in their power to be free from the bondage of repeated births and deaths.

Then there is no need for the scriptures, religion, and idea of God. One has to be more rational to realize the Advaitic truth, which is the ultimate truth or scientific truth. 

Remember:~ 

The scriptures are for ignorant masses, who wholly accept the material world as it presents itself. Non-dualistic or Advaitic wisdom is for those who have begun to realize that things are not what they seem.

Even the Upanishads are Self-contradictory. Pundits and scholars give conflicting interpretations of them. When one uses his own Common-sense he becomes aware that, the final authority, therefore, is using his own reason. One should apply his reason to the scriptures before accepting them as truth.

Astavakra: ~ “My child you may speak upon various scriptures or hear the sermons on the scriptures. But you cannot establish the ‘Self’ unless you forget all. 16-1 – p49

Sages of truth restrained themselves parting the Self-knowledge or Brahma Gnana or Atma Gnana to the mass and only a selected few. It was hidden from the people who were not qualified and receptive to it. Self’ - knowledge or Brahma Gnana or Atma Gnana was not written down but was imparted orally to the chosen few.

Thus, religion was given to the mass, and knowledge of the Spirit is given to only a selected few. Thus, we find traces of the knowledge of the spirit in the religious books in the form of parables.

Swami Vivekananda: ~ “Advaita encompasses everything. Since Advaita requires heavy-duty intellectualism, it had to be progressively simplified. (From 'The Complete Works of Swami Vivekananda)

Self-Knowledge or Brahma Gnana or Atma Gnana is not based on any teaching or teacher.  The Pursuit of truth is the pursuit of verification not the pursuit of an argument.   Intellectual discussion is a great hindrance in the pursuit of truth.

That which is unreal, that is duality, cannot contradict the truth of non-duality. It cannot be counted as an adversary of non-duality. The illusion cannot, 'oppose' the substratum, reality. It can at best lead to the mistaking of the substratum. Perfect understanding is the only way to overcome ignorance. : ~ Santthosh Kumaar