Rama and Hanuman of the Hindu Epic Ramayana, in Muktika Upanishad, discuss moksha (freedom, liberation, deliverance). Rama, therein, recommends Mandukya as first among 108 Upanishads, as follows,
The Mandukya alone is sufficient
for the deliverance of the aspirant,
if even then, the knowledge lacks,
then read the ten Upanishads.
He attains the goal
if he reads the thirty two Upanishads,
if you just wish deliverance, while death is near,
read, then, the hundred and eight Upanishads.
— Muktika Upanishad I.i.26-29,
Mandukya Upanishad (Sanskrit: माण्डूक्य उपनिषद) is famous theory of the state of consciousness. It contains the epitome of the substance of the import of Vedanta. It also contains eternal spiritual laws discovered by sages. It has been said that the essence of the Vedas is in the Upanishads, and the essence of Upanishads is in the Mandukya Upanishad.
In Mandukya, Om is bow, the soul is the arrow and Brahman (God) is the target. The target is to be hit by an unerring person. One should become one with the target just like the arrow. The teachings of the Mandukya Upanishad are well worth deep study, discussion, reflection and contemplation. By faithfully and intently engaging these twelve verses, all of the other written and oral teachings can be explored as expansions of the foundation principles and practices encapsulated in this succinct summary.
Verses of Mandukya Upanishad: Verses 1-2 describe the Self and the Absolute. Verses 3 to 7 explain the four levels of consciousness and verses 8 to 12 outline the four aspects of ‘AUM’.
“AUM, the world, is all this”. The mind should be concentrated on ‘AUM’. ‘AUM’ is the fearless Brahman. He who is always absorbed in AUM knows no fear whatever. The whole universe is the syllable ‘Om’. ‘Aum’ stands for supreme reality and it is a symbol for what was, what is and what shall be. ‘Aum’ represent also what lies beyond past, present and future.
Four levels of consciousness (3 to 7 verses): In this first aspect of Atman (Self in the walking state, Vaishvanara), Consciousness is turned outward to the eternal world. It experiences the gross objects of the phenomenal world. In this second aspect of Atman (Self in the dreaming state, Taijasa), Consciousness is turned towards the inner world. In this third aspect of Atman (Self operating in the deep sleep state, Prajna), In this state, there is neither the desire for any gross nor any dream sequence. In this fourth aspect of Atman (Turiya), in this state, consciousness is neither turned outward nor inward. It is pure consciousness itself. This is the real self. This is the real or true Self that is to be realized.
Four aspects of ‘AUM’ (8 to 12 verses): The three sounds A-U-M (AH, OU, MM) and the three letters A(अ ), U(उ), M(म) are identical with the three states of waking, dreaming, and sleeping. Vaishvanara is the consciousness experienced during the waking state. ‘A’ is first letter of Om. He who knows thus, does verily attain all desirable things, and becomes the foremost.
The dreaming condition, called the mental condition, corresponds to the second letter U. It upholds; stands between waking and sleeping. He who understands, upholds the tradition of spiritual knowledge; looks upon everything with an impartial eye.
The deep-sleep state, the cognitional, is the letter M. It weighs and unites. He who understands, weighs the world; rejects; unites himself with the cause.
The last aspect of Om is soundless. It is not utterable and is not comprehended through the senses or by the mind. This state is true real self.
Mandukya Upanishad is complete outline for sadhana, Meditation, enlightenment practices. The Om Mantra is a roadmap of the entire process of Meditation and a most practice tool for Self-realization. Mandukya Upanishad is sufficient for realization.