Sage Sankara:~ Actual realization takes you beyond books.+

There has never been a single scripture that has the whole wisdom in it. Sage  Sankara restrained himself parting the Advaitic wisdom to the mass and imparted only to a selected few. 

Advaitic wisdom was hidden from the people who were not qualified and receptive to it. 

Advaitic wisdom was not written down in one book but was imparted orally to the chosen few. Thus, religion was given to the ignorant populace and the Advaitic wisdom is given to only a selected few.

Thus, we find very few traces of Self-knowledge in the religious books in the form of parables. 

Sage Sankara says: ~ A buried treasure is not uncovered by merely uttering the words: “Come forth.” You must follow the right directions, dig, remove the stones and earth from above it, and then make it your own. In the same way, the pure truth of the Atman, which is buried under Maya and the effects of Maya, can be reached by discriminating between real and unreal, and renouncing the false is real meditation, 

Bhagavad Gita says: ~ Among thousands of men, scarcely one strives for perfection; and of those who strive and succeed, scarcely one knows the ‘Self’ in truth.

Sage Sankara:~ 'Like a servant who carries a lamp in front of you to find your way, and you have found it, so becomes the Veda to that person. What is the Veda? ~ utterances of those who have known the Truth. Here is one who has known the Truth; why should he or she depend upon the Veda further? Actual realization takes you beyond books. At a certain stage, books become a botheration. The Upanishad itself says that the 'words are only so much of the  distraction for such minds.'

The man who possesses the highest intellect can grasp Advaita, by merely hearing the truth mentioned and will know it.

Bhagavad Gita: ~ Reason as means to reality. (Chap.18 verse 37)

In chap. 10 of the Bhagvad Gita, Krishna says: ~ I cannot save you, but I can give you Buddhi (reason). (chap. 10)

In chap. 10 of the  Bhagavad Gita, Krishna says: ~ "I have given you the most secret teaching, now reflect over it all" Krishna plainly says reflect, think. (Verse 63 of Chap. 18)

Mundaka Upanishad says: ~  Both states are harmful and take you away from the path of inquiry into the truth. (Page 234)

Ashtavakra Gita: ~ It is not the absence of Buddhi (Reason) that can grasp Advaita, but the man who possesses the highest intellect. Brains are necessary. Such a man, by merely hearing the truth mentioned will know it. (Page~ 224).

The mystic must become a constant slave to some line of "thought" or rather imagination, and then he will really see visions confirming his imaginations.

The mystic who sees God in the vision has seen Him during the waking state. The waking experience itself is an illusion. Thus, whatever is seen within the illusion is bound to be an illusion. Thus, it is necessary for the mystic to realize his existence is a reality within the illusion. 

Whatever belief of God one is familiar with through his inherited conditioning or samskara that he will see in his visions.  When the man is the false Self within the false experience, then whatever he believes is bound to be a falsehood. 

God is the Soul, the Self.  The Soul is present in the form of consciousness. God is not within you, but you and your experience of the world are within God.  Self-realization is God-realization because the Soul, the Self itself is God in truth.  

When you and your experience of the world disappear, then God alone prevails as the formless, timeless, and spaceless existence. :~Santthosh Kumaar