The seeker, Bhrigu, in the Taittiriya Upanishad is sent back after his realisation of the physical Self, for further concentration. His next realisation brings him to the Vital Self, the Self consisting of Prana. We see in the world of Matter that the vital energy, the life force, arises in a portion of the physical Matter that has been prepared for its emergence. This vital energy begins to redirect and change the nature of pure Matter. As it grows and develops, it takes on characteristics that approximate its natural action in the vital world, seeking and desiring, acquiring and enjoying. There are worlds that are predominantly vital worlds that are not bound by the limitations of the physical world of Matter and in these worlds, the vital principle is supreme in its action.
Sri Aurobindo elaborates: “But the Spirit can be poised in the principle of Life, not in Matter. The Spirit so founded becomes the vital self of a vital world, the Life-soul of a Life-energy in the reign of a consciously dynamic Nature. Absorbed in the experiences of the power and play of a conscious Life, it is dominated by the desire, activity and passion of the rajasic principle proper to vital existence….The physical element in a vital world readily shapes its activities and formations in response to desire and its imaginations, it serves and obeys the passion and power of life and their formations and does not thwart or limit them as it does here on earth where life is a precarious incident in inanimate matter. The mental element too is moulded and limited by the life-power, obeys it and helps only to enrich and fulfil the urge of its desires and the energy of its impulses. This vital soul lives in a vital body composed of a substance surcharged with conscious energy, capable of much more powerful perceptions, capacities, sense-activities than any that the gross atomic elements of earth-matter can offer.”
“Man, too, has in himself behind his physical being, subliminal to it, unseen and unknown but very close to it and forming with it the most naturally active part of his existence, this vital soul, this vital nature and this vital body; a whole vital plane connected with the life-world or desire-world is hidden in us, a secret consciousness in which life and desire find their untrammelled play and their easy self-expression and from there throw their influences and formations on our outer being.”
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 21, The Ladder of Self-Transcendence, pg. 449