Mundaka Upanishads:~ So-called spiritual pundits and learned are called children because a child takes whatever it thinks as 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) Vivekachoodamani v 56, pg~25

Mundaka Upanishad condemns rituals. The Para or Higher knowledge is the knowledge of the Supreme Being, while the Apara or Lower Knowledge is that of following sacrificial rites and ceremonies. (1/2/ 1 – 6)

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

Lord Krishna confesses that the oldest wisdom of India (our true Advaita philosophy) has been lost: people misinterpret and falsify it today as they did then. It is not yoga but the philosophic truth. But nobody knows it. The teachers of philosophy and leaders of mysticism or religion do not want to inquire into truth and have no time for it. (Gita –Chap- IV-v.2)

Mundaka Upanishad~ “The study of the Vedas, linguistics, Rituals, astronomy and all the arts can be called lower knowledge. The higher is that which leads to Self-realization. The eye cannot see it; the mind cannot grasp it. The deathless 'Self' has neither caste nor race, neither eyes nor ears nor hands nor feet. Sages say this Self is infinite in the great And in the small, everlasting and changeless, The source of life.

There is no need for a Guru in the Atmic path.

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.”

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 formless Soul, which is present in the form of consciousness.

In the realm of truth the form, time, and space are created out of single stuff. That single stuff is consciousness. Realizing the single stuff as ultimate truth is Self-realization or truth realization. To realize this truth, there is no need for scriptures.  

This Atman cannot be attained by the study of the Vedas, or by intelligence, or by much hearing of sacred books. It is attained by him alone whom It chooses. To such a one Atman reveals Its own form. (Katha Upanishad Ch-II -23-P-20)

Mundaka Upanishad: - This Atman cannot be attained through the study of the Vedas, nor through intelligence, nor through much learning. He who chooses Atman—by him alone is Atman attained. It is Atman that reveals to the seeker Its true nature. (3 –page-70 Upanishads by Nikilanada)

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 the invisible Soul, which is present in the form of consciousness. 

In the realm of truth the form, time, and space are created out of single stuff. That single stuff is consciousness. Realizing the single stuff as ultimate truth is Self-realization or truth realization.

To realize Advaitic truth, there is no need for scriptures. :~Santthosh Kumaar