Sri Aurobindo translates Taittiriya Upanishad, Brahmanandavalli, Chapter 3 (part 2): “Now there is yet a second and inner Self which is other than this that is of Prana, and it is made of Mind. And the Self of Mind filleth the Self of Prana. Now the Self of Mind is made in the image of a man; according as is the human image of the other, so is it in the image of the man. Yajur is the head of him and the Rig-Veda is his right side and the Sama-veda is his left side: the Commandment is his spirit which is the self of him, Atharvan Angiras is his lower member whereon he resteth abidingly. Whereof this is the Scripture.”
At the next subtler level, the Upanishad reveals a Self of Mind, which fills, informs and directs the action of the vital and material sheathes. The Self of Mind operates under its own principles of action, modifying the action of the vital and the material levels, and in turn, being modified and limited by the limitations of those two levels.
Sri M. P. Pandit explains: “Wherever this is life, there is behind it an operating consciousness which in its awakened form is termed Mind, manas. And the Atman as the Self of this Mind-plane of existence is called the manomaya purusa. This Mind-being is the leader of the life and body, prana sarira neta, as another Upanishad puts it.”
“This Purusha of the Mind, says the Upanishad, is constituted of the stuff of the Eternal Word in expression in Creation …. The Word of Illumination and the Word of Harmonies are its twin sides and the Word of Execution is its head. The vidhi, an imperative Directive to ever sacrifice and progress is its centre and a settled, fixed flame of Aspiration is its urging base.”
Sri Aurobindo, in On Yoga, as cited by M. P. Pandit explains further: “Above matter and life stands the principle of mind, nearer to the secret Origin of things. The Spirit poised in mind becomes the mental self of a mental world and dwells there in the reign of its own pure and luminous mental Nature. There it acts in the intense freedom of the cosmic Intelligence supported by the combined workings of a psycho-mental and a higher emotional mind-force, subtilised and enlightened by the clarity and happiness of the sattwic principle proper to the mental existence. In the individual the spirit so poised becomes a mental soul, manomaya purusa, in whose nature the clarity and luminous power of the mind acts in its own right, independent of any limitation or oppression by the vital or corporeal instruments; it rather rules and determines entirely the forms of its body and the powers of its life. For mind in its own plane is not limited by life and obstructed by matter as it is here in the earth-process.”
“It is possible for man to awaken to this higher mental consciousness, to become this mental being, put on this mental nature and live not only in the vital and physical sheaths, but in this mental body.”