These bodies of the eternal, indestructible and enlightened Spirit are called perishables ...
It is neither born nor dies; nor having existed ceases to exist, never again.
Unborn, perpetual, eternal, ancient, is not killed when the body is killed.
Bhagavad Geeta, 2, 18-20

1. Supreme Bliss can not be experienced in the contact of the senses with their objects. The supreme state is one in which the mind is annulled by means of focused research.
2. The joy produced by the contact of the senses with their objects is inferior. Contact with objects is slavery, to free oneself is liberation.
3. Come to the pure state between existence and inexistence and remain us; do not accept or reject the outer world or the inner world.
5. Believing an acquaintance and a known is slavery; the acquaintance is a prisoner of the known; it is liberated if there is nothing to be known.
10. Who meditates on the state that is the boundary between waking and sleep, directly experiences an incorruptible ananda (bliss).
Yoga Vasishta Sara, ch. X, 'Nirvana'

Asato ma Sat gamaya
Lead me from falsehood to Truth
Tamaso ma Jyothir gamaya
Lead me from darkness to Light
Mrtyor ma Amrita gamaya
Lead me from death to Immortality!
Brhadaranyaka Upaniṣad, 46, IV

1. Atmaivedamagra asit purusavidhaha
So anuviksya na anycilh atmano apasyath.
Sa aham asmithyagre vyahrath, tato aham anamabhavath;
thasnzadapyetharhminthritho aharnayamithyevagra ukthva athanyannama prabhrute yadasya bhavati;
sa yatpurva asmathsarvasrnath srvanpapmana ausath thasrnatpurusaha, osatlziha vai sa tham yo asmath purvo bhubhhusathi ya evam veda.

In the beginning there existed only the Atman (the immanent Cosmic Self) in the form of the Cosmic man (Puruṣa) - Looking around he could not see Himself. Then, That uttered this word: I AM (the Word of words, the Logos): I AM ALL OF THIS. From this statement the term IO (Aham) was born - So even today, when someone calls, the answer is "I am", and only then are the other names. It is called Puruṣa ("the Lord of the City": Puru = city and Sa = Lord: of the "nine-door city" which is the human body with its nine orifices). Anyone who conceives of the "I" in this way will burn all ills.
In the cosmogenesis of the Upaniṣad, the universe is only the reflection of the Cosmic Self, the Ocean of I AM. The Mosaic revelation on Sinai: "I am He who I Am, He who is called Thee has sent me to you") is very close to the concept that only the Cosmic Self is real: the God of Moses, of Abraham, of Isaac, of Jacob, of Muhammad and of Abu Bekr. In the Zoroastrian tradition, the only Reality is Sarvan Akaran, the Uncaused Cause of Everything; the conflict between Good and Evil, symbolized in the struggle between Ormuzd (Ahura Mazda) the principle of Good and Ariman the principle of Evil, Satan, begins with the Creation which, in the Indoarian tradition, is only the projection of names and forms on this Ocean of I AM, that is the Atman immanent in the whole Universe, which also transcends it as Brahman. The conflict between Good and Evil is resolved only in the Cosmic Self, in the I AM, where all forms of duality are transcended in the unifying consciousness of the I AM. To bring oneself to It and to remain there is Liberation, Illumination and ineffable Bliss.
Primordial matter (with its physical, subtle and causal bodies) is perishing; instead God (the Brahman together with His creative power, Maya) is imperishable. God, God alone is He who governs both the matter perishing and the individual souls. The only way to put an end to all sorts of illusions (produced by Maya) is meditation on God, the effort to go to Him and unite; identifying with Maya, creative power, casts a spell on all the beings that are born, presenting them the illusory world as real and the real world as illusory. This cosmic illusion operates in every field of life. The center and the circumference of illusion is the ego, the consciousness of the "I" that, separating itself from the Eternal and from every other being, pushes to lead a life focused on the ego, with the consequent errors and passions that tighten moreover to cosmic illusion. Ignorance, egoism, pain, maya are synonymous, related to various ways of considering the unreal, changing and perishable world. The only way to free ourselves from the snares of illusion is meditation and reflection, which Vedanta calls manana. Manana is the second of the three phases: Sravana, Manana e Nidhidyasana: listening, reflection or meditation on the word of God, experience and, finally, Realization of the truths heard, on which one is meditating. It is necessary to cross the world of duality with unified contemplation, transcend it with meditation, discriminating between the unreal and the Real, between the ephemeral and the Eternal in order to cut off the pains of duality and multiplicity.
11. Jnatva devam sarvapasapahanihi
Ksinaì ha kleshairjanmamritiyuprhanihi

The appearance of the unitive knowledge of God breaks all the chains (of our heart). This knowledge dispels ignorance and stops the wheel of births and deaths. By overcoming the consciousness of the body (identification with the mortal body) on the path of meditation, the third stage is reached, which is the lordship over all Creation. By identifying with God, who is the One without a second, all the wishes of the Heart are fulfilled. Since the conscious mind vanishes in deep sleep, and reappears in the states of dreaming and waking, it is evident that the mind continues to exist consciously and unconsciously in this particular body or some other incarnate state. When the consciousness lives in a limited body, which has come into the world at birth and which will disappear with death, it is in the world of illusion and moves in it, accepting the multiplicity and the dualities of the world as final and real. This spiritual ignorance born of identification with the bodily envelope and the mind is the cause of Samsara, of the incessant transmigration of the soul from one body to another, from one birth to another. This process can only be stopped by the rays of the knowledge of the Self, to be reached through the search for "who am I?" and the discovery of our innate identity with the Real, with the Eternal, with God; discovery that puts an end to all our pains and our crying. The only way to liberation is the unified contemplation, which transcends the pluralistic world with meditation and discrimination between the True and the false.
12. Etat jneyant nityam eva atmasarnstham
Nata/la paramveditavyam lii kincith
Bhokta bhogyam preritaratfl cci matva
Sarvam prolctam trividham brahmametat.

One must know with certainty that God exists eternally as our inner Self. Beyond that there is absolutely nothing to know; but we must have experimental knowledge. With meditation we can come to realize that the mind, the matter and the Maya (the subjective conscious power, the objective phenomena and the power that binds the subject and the object), are three aspects of Brahman himself, of Reality.
Svetasvatara Upaniṣad, Part Four

OM Pūrnam-Adah Pūrnam-Idam Pūrnāt-Pūrnam-Udacyate
Pūrnasya Pūrnam-Ādāya Pūrnam-Eva-Avashissyate
OM Shāntih Shāntih Shāntih!

This (Supreme I) is fullness (infinite), This (Universe) is fullness (infinite). From this infinite I (the Absolute), the unconditioned, this cosmos (the relative), the conditioned, has emerged (emanated). I draw this Infinite from that Infinite (the Absolute), what still remains is the Infinite. OM, Peace, Peace, Peace!
The upanisadic prophet from the supreme peaks of the contemplative vision pronounces certain phrases that, for the common vulgar, sound meaningless, while for scholars they express the highest divine wisdom.
In this opening verse we are told that the Absolute and the relative, the unconditioned Being and the conditioned becoming are only the sides of the same coin. There is nothing but a Supreme Reality, Brahman, the objective Universe, the Ātman, the Universal Subjective Subject, psychologically realized by the sage through inner discipline and intense meditative concentration. The universe is none other than Brahman, and Brahman is none other than Ātman, and Brahman and Ātman togheter represent the absolute Being, the supreme Reality considered from two different points of view. Infinity has no parts, for it is One, the One without a second and, as such, the coming out of the universe takes nothing away from the infinity of the Supreme Being. Although, empirically, an apparent duality is present in the sensory experience between the infinite Essence of God, the Absolute, the Ātman and the Cosmos, speaking in ontological and reality terms, there is an absolute identity between the Cosmos and absolute Reality.
52 (23). Na ayam āttnā pravachanena labhyo
Na medhayā ira bahunā srutēna
Yam evai esha vrunute tena labhyah
Tasyai eshā ātmā vivrunute tanūm svām
.
Through the study of the scriptures alone or through erudition one can not realize the Superanima, or even through academic intellectualism, nor the debates in the classroom. But he who seeks it passionately, is able to know God. In fact, he manifests himself to these devotees (ardent aspirants), who thirst for Him.
Iṣa Upaniṣad

33 (1). Avih sannihitam guhacharam nama
Mahat padam atra etat samarpitam
Ejat pranam nimisha cha yad etat janatha sada
sadvarenyam param vijnanad yad varishtham prajnanam
.
The Supersoul is self-luminous in itself and reigns in the heart of every man. It is the supreme end of everything. In the womb of the Ego, everything moves, that which moves and that which is immobile in the Universe, comes to life. Everything lives inside him, raw or subtle. He transcends logical and discursive thinking. It is the Most High, the object of the greatest desire, and to know Him means to find true life.
34 (2). Yadarchimadyadanubhyo'nu cha
Yasmim loka nihita lokinashcha
Tadetadaksharam brahma sa pranastadu vanmanah
Tad etat satyam tad amrutam
Tad veddavyam somya viddhi.

Brighter than the light, thinner than the thin, this is how the ego on which the galaxies are fixed and all those who live there, as the spokes of the wheel are fixed on the axis. This Supersoul is called imperishable Brahman and is the Life of every life. He is existence itself, brilliant, true, immortal. And it is this super-soul that you, courageous disciple, must strive to understand, making sure that your Heart aims at this single target.
36 (4). Pranavo dhanuh sharo hyatma brahma tat lakshyam uchyate,
Apramattena veddhavyam sharavat tanmayo bhavet
.
The arch symbolizes the AUM. The arrow indicates the intellect in one direction with the mind and the Heart. Ātman is the target. One who will be freed from the desire to enjoy external objects, will be able to aspire totally to Brahman and identify with him, like the arrow that, striking the target fully, becomes one with it. Here we want to indicate that Brahman could be desired to the point of being able to conquer it, only when the passions have subsided and the desire for external objects has fallen, reaching the tranquility of our Heart.
37 (5). Yasmin dyauh pruthivi cha anatarikshamotam
manah saha pranaishcha sarvaih
Tamevaikam janatha atmanamanya vacho
vimunchath amrutasyaisha setuh.

The heavens, the earth and the interposed areas of the exterminated space all have the ego at the core. Know that even the mind and the senses and all the vital organs have been elaborated in this ego. Fight to know Him alone, all the rest is in vain. He is the bridge (between this land of mortals and farther beaches) of Immortality.
Mundaka Upaniṣad Canto 11

1. Om ityetadakṣaraṃ idaṃ sarvaṃ tasyopavyākhyānaṃ
bhūtaṃ bhavad bhaviṣyaditi sarvam Omkāra eva.
Yaccānyat trikālātītaṃ tadapyomkāra eva
.
The whole universe is nothing but AUM, a symbolic imperishible syllable that stands for Brahman. All that existed, all that exists and that will exist is in reality not that AUM. Whatever one thinks in the guise of present, past or future, is also AUM. There exists a only, single Reality in the Supreme Being which, enclosed within the limited and conditioning factors of the senses and of restricted reasoning based on the life of the senses, appears, under different forms and multiple aspects, all reduced within the categories of time, space and cause, as well as within those of names and forms. What transcends every limitation and classification of names and forms, of time, cause and space, which lies beyond the past, present and future, is this single Reality, the unique Being, the Essence of God, God himself who takes the various appellations of Allah, Elohim, Tao, Brahman, Ātman and AUM, which is the vibrating Vedic symbol of the infinite Being which is Brahman. Beyond this there is nothing else, and the whole Universe, the cosmos, is nothing but a Brahman conditioned and imprisoned within forms and names.
2. Sarvaṃ hyetad brahmāyamatma brahma so'yamatma catuṣpāt.
The cosmos is Brahman. The Self itself is Brahman. (The objective cosmos is the One, Brahman and the subjective soul is also Brahman, both the inner and the outer world are Brahman, Ātman, Supersoul). This Self presents four different states of being. (Brahman exists in four ways, four states of mental awareness).
Māṇḍūkya Upaniṣad