The Mandukya Upanishad is, indeed, the shortest one among the key principal Upanishads, having the most extensive and elaborate contents dealing with some profound principles of Hindu philosophy. For anyone wishing to get acquainted with Hinduism or to take recourse to its spiritual practices, this text gives some extraordinary insights into the nature of consciousness and reality.

The Structure and Scope 

 It belongs to the Atharva Veda, having only twelve verses, and its special peculiarity is the extreme brevity. An ancient Sanskrit saying states: "मण्डूक्यमेकमेवालं मुमुक्षूणां विमुक्तये" (Mandukya ekam eva alam mumuksunam vimuktaye) - "The Mandukya alone is enough for liberation for those who seek it." 

The Sacred Syllable OM

Through the syllables of the sacred OM, the Mandukya Upanishad begins its exposition: 

 "OM – this syllable is all this. An explanation of that: All that is past, present, and future is indeed OM. And whatever else is beyond the threefold time, that too is OM." (Verse 1)

This first statement epitomizes the investigations of the Mandukya into how this single sound encompasses absolutely every possible bit of existence and consciousness.  

 The Four Modes of Consciousness

The request for the Mandukya to systematically approach consciousness through its four states remains a unique contribution of Hindu philosophy

 Waking State (Vaishvanara)

"The first quarter is Vaishvanara, whose sphere is the waking state, who is conscious of the external world, who has seven limbs and nineteen mouths, and who enjoys gross objects." (Verse 3)

This represents the mundane state of waking consciousness engaged in a physical world through objects of sensation. 

Dreaming State (Taijasa)  

"The second quarter is Taijasa, whose sphere is the dream state, who is conscious of internal objects, who has seven limbs and nineteen mouths, and who enjoys subtle objects." (Verse 4)

This denotes consciousness directed inward, aware of worlds founded on mental images and impressions.  

Deep Sleep (Prajna)  

"The third quarter is Prajna, whose sphere is deep sleep, in whom all experiences become unified, who consists of bliss, who is the enjoyer of bliss, and who is the doorway to the knowledge of the two other states." (Verse 5)

This is the consciousness in its potential form, untouched by differentiation or duality. 

Turiya (The Fourth)

"That which is not conscious of the internal world, nor conscious of the external world, nor conscious of both the worlds, nor a mass of consciousness, nor simple consciousness, nor unconsciousness; which is unseen, ineffable, ungraspable, devoid of characteristics, unthinkable, unnameable, whose essence is the experience of its own Self, in which all phenomena cease, which is peaceful, all-blissful, and non-dual-that is the fourth quarter. That is the Self. That is to be known" (Verse 7). 

This state is not actually a "state" but is the reality that underlies and supports all states: pure consciousness. 

 Mystical Analysis of OM

The four states of consciousness just described are then associated with the three letters of the sacred syllable OM (A-U-M) plus the silence that follows:

"The letter A represents Vaishvanara... The letter U represents Taijasa... The letter M represents Prajna... The measureless is Turiya." (Verses 9-12)

This not only lays down a conceptual understanding but also serves as a practical method of meditation where the aspirants can use the sound OM to travel along the various levels of consciousness toward the final realization.   

Practical Applications for the Spiritual Seeker

The Mandukya Upanishad affords various approaches to those wishing to adopt Hindu spiritual practices:

OM Meditation: Using the sacred syllable as a vehicle to explore different states of consciousness Self-Inquiry: Investigating the nature of your awareness in waking, dreaming, and deep sleep Witness Consciousness: Cultivating awareness of the "fourth" state that transcends yet permeates all other states

Non-Dual Awareness: Recognizing that Atman (individual self) and Brahman (cosmic Self) are identical

Further Study Resources

For more information regarding this profound text:

The Mandukya Upanishad, with Gaudapada's Karika and Shankara's Commentary translated by Swami Nikhilananda 

Eight Upanishads with the Commentary of Shankaracharya translated by Swami Gambhirananda  

The Principal Upanishads by S. Radhakrishnan  

The Upanishads: Breath of the Eternal by Swami Prabhavananda and Frederick Manchester  

The Mandukya Upanishad is studied together with Gaudapada's Karika, the verses of exposition that develop the Upanishad's teachings in terms of the philosophy of Advaita Vedanta. This joint text forms the approach to the understanding of non-duality in Hindu thought. 

While certainly concise, the Mandukya Upanishad serves as one of the most thorough inquiries into consciousness in world spiritual literature. Its graceful transition from ordinary waking states to the transcendental "fourth" affords the double advantage of intellectual comprehension and details of practice for those truly seeking the highest knowledge in the Hindu tradition. By contemplating the verses and practicing OM meditation, seekers go deep into their consciousness, discovering that underlying the entire fabric of all experience is the non-dual reality.