Sage Goudpada was the first historic teacher known to us to give a rational exposition of Advaita.+

Mundaka Upanishads:~ So-called spiritual pundits and learned are called children because a child takes whatever it thinks as truth. The question never occurs in children “Is what I have seen or thought really the truth?" (P.334 line 9)

The scriptures are not needed in the 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 formless Soul which is present in the form of consciousness. 

In the realm of the truth the 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 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 citation only after verifying reality and proved the truth, to point out that the scriptures teach the same thing. If one quotes them before having demonstrated truth, then it is scholasticism.

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 other scriptures in order to acquire non-dual wisdom.  That is why 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 the religion.  Self-discovery is the only way, towards 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. 

Sage  Goudpada was the first historic teacher known to us to give a rational exposition of Advaita. He says that whatever is seen, whether external or internal, whether by the ordinary persons or yogis is unreal.

Non-causality is of the highest importance; that is why Sage Goudpada puts it at the end of his book and devotes 100 slokas to it whereas the other subjects get less than 50 slokas.

Manduka Upanishad shows how one opinion may be used to contradict another, so that both may be thrown away. Opinions are not for philosophy; Ashtavakra says they are merely thoughts; not the truth.

Manduka Upanishad has no assumptions, whatever. It is an honest and bold inquiry into the truth. It rises above scripture.

Manduka Upanishad is not meant for all, as it is based entirely on the reasoning. Hence, only a few will be able to understand and assimilate it.

Manduka Upanishad:~ Atman is the highest Reality and its opposite: Note the word "and". Reality and illusion together make Brahman: nothing can be left out.  Page 51.

Brahman must be realized in the waking state when all objects are present to consciousness, otherwise, it is nonsense. Page 65: v.10.

"Sleep does not exist In Turiya”: This emphatically disproves the mystic use of sleep as an analogy for Brahman. Page 69.

This means that objects do not disappear, they are there, and yet they are non-dual. Disillusionment is not the same as appearance. Page 74. v. 17:

The essential message of Manduka is that the whole world, whatever is seen is only imagined.  Points out that even though it is harder for them, still women can attain Brahman just as men. Page 351points out that even though it is harder for them, still women can attain Brahman just as men. Page 351

"From their notion": Everybody has his own imagination about facts and starts from that, instead of discarding his personal idea and looking at the fact. Page 333. V. 83:

"Soundless and of infinite sounds"; means both waking and sleep world must be known, both objects and non-objects must be understood before the truth of Brahman is realized. Page 96. v. 29:

In deep sleep and anesthesia you have non-duality,  but no Gnana. Therefore,  there must be discrimination along with non-duality. Otherwise, sleeping dogs would be Gnanis. ~ (P.219)

Existence means existence in the sense of the Drik. When you reduce everything to consciousness, Drik, Gnana, or even Mind, giving up all imaginations in truth it is unborn. You see a man's body comes and goes, but that is not the same as seeing him come and go, which you can never do. P.300. V.45.

Sage Goudpada 's 3^rd chapter is devoted to proving  the existence of Atman in order to distinguish it from the changeable objects in this world, but in the final 4th chapter P.33, verse 

83, he discards that position and rejects even the idea of Atmanic existence. He then declares we may assert nothing about it. Not even existence or nonexistence i.e. silence alone is demanded by the truth.

Advaita is not philosophy but Advaita is the nondual nature of the Soul. There is no second thing that exists other than the Soul, which is present in the form of consciousness.  At that ultimate understanding - there is only self-awareness. Existence-consciousness cannot be divided. If one sees divisions they are only apparent and not real. If one takes the apparent as real, then all other factors become real.:~Santthosh Kumaar