As Bhrigu continued his concentration to determine the Eternal, he passed beyond the world of Prana, the vital world and next concluded that it was Mind that was the source of all. Similar conceptions have arisen in Western philosophy from time to time, with the famous aphorism of Rene Descartes “I think, therefore I am” representing a realisation that placed Mind at the center of conscious awareness and meaning in the world. The human individual who passes beyond total involvement in the physical life of Matter and the vital life of desire can enter into a mental world and framework that has more flexibility and power to adapt, change and develop.
Sri Aurobindo describes the Mental Self: 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 purusha, 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. This mental soul lives in a mental or subtle body which enjoys capacities of knowledge, perception, sympathy and interpenetration with other beings hardly imaginable by us and a free, delicate and extensive mentalised sense-faculty not limited by the grosser conditions of the life nature or the physical nature.”
Sri Aurobindo, The Synthesis of Yoga, Part Two: The Yoga of Integral Knowledge, Chapter 21, The Ladder of Self-Transcendence, pg. 451