WISDOM IN UPNISHADS

Not through much learning is the Atman reached, nor through the intellect and 'the sacred teachings. It is reached by those whom He chooses; to His chosen the Self reveals His glory.
Beyond the senses is the mind, beyond the mind is the intellect, higher than the intellect is the Great Atman [the totality of all minds], higher than the Great Atman is the Umanifest. Beyond the Unmanifest is the Person, all-pervading, and imperceptible.
Smaller than the smallest, greater than the greatest, this Self forever dwells within the hearts of all. When a man is free from desire, his mind and senses purified, he beholds the glory of the Self and is without sorrow.
Though seated, he travels far; though at rest, he moves all things. Who but the purest of the pure can realize this Effulgent Being, who is joy and who is beyond joy.
Formless is he, though inhabiting form. In the midst of the fleeting he abides forever. All-pervading and supreme is the Self. The wise man, knowing him in his true nature, transcends all grief.
*Kathopanishad
As long as there is duality, one sees "the other," one hears "the other," one smells "the other," one speaks to "the other," one thinks of "the other," one knows "the other"; but when for the illumined soul the all is dissolved in the Self, who is there to be seen by whom, who is there to be smelled by whom, who is there to be heard by whom, who is there to be spoken to by whom, who is there to be thought of by whom, who is there to be known by whom? Ah, Maitreyi, my beloved, the Intelligence which reveals all--by what shall it be revealed? By whom shall the Knower be known? The Self is described as "not this, not that" (neti, neti). It is incomprehensible, for it cannot be comprehended; undecaying, for it never decays; unattached, for it never attaches itself; unbound, for it is never bound. By whom, O my beloved, shall the Knower be known?
* : Bhrihadaranyaka
If you think that you know well the truth of Brahman, know that you know little. What you think to be Brahman in your self, or what you think to be Brahman in the gods--that is not Brahman. What is indeed the truth of Brahman you must therefore learn.
I cannot say that I know Brahman fully. Nor can I say that I know Him not. He among us knows Him best who understands the spirit of the words, "Nor do I know that I know Him not."
He truly knows Brahman who knows Him as beyond knowledge; he who thinks that he knows, knows not. The ignorant think that Brahman is known, but the wise know Him to be beyond knowled
* Kena
The door of the Truth is covered by a golden
disc. Open it, O Nourisher!
Remove it so that I who have been worshipping
the Truth may behold It.

O Nourisher, lone Traveler of the sky! Controller!
O Sun, offspring of Prajapati! Gather Your rays;
withdraw Your light. I would see, through Your grace,
that form of Yours which is the fairest.
He, that Person who dwells there--is I myself!
* Isha
Dwelling in every heart,
the Self is the Lord of all,
the seer of all,
the source and goal of all.
The Self is not outer awareness,
It is not inner awareness,
Nor is it the suspension of awareness.
It is not knowing,
It is not unknowing,
Nor is it knowingness itself
It cannot be seen nor grasped,
It cannot be contained.
It is beyond all expression and beyond
all thought.
It is indefinable.
The only way to know it is to become
* Mandukya