Sri Aurobindo translates Mundaka Upanishad, Chapter 2, Section 2, verse 8: “A mental being, leader of the life and the body, has set a heart in matter, in matter he has taken his firm foundation. By its knowing the wise see everywhere around them That which shines in its effulgence, a shape of Bliss and Immortal.”
The Western approach, enshrined in both the scientific and philosophical disciplines, to the existence of the human being, the “mental being”, has mainly been based on the idea that Matter came first, and somehow, through random chance or some kind of chemical reactions, life, and mind eventually resulted. The approach of the Bible was a miraculous creation by an external God of a fully formed human being made out of clay and a subsequent eating of the fruit of the tree of knowledge of good and evil to develop the analytical mental capacities. Mythological stories tell of a forerunner, a Prometheus, who stole fire from the Gods for the sake of humanity. All of these approaches treat the mental capacity as somehow arising from material existence without any realistic “cause”.
The Upanishad takes a different approach, as it indicates that the mental being essentially preexists the material and vital foundation and shapes these to its requirements. This implies that nothing can “evolve” out of Matter that is not already “involved” in Matter. The analogy of the seed, having the tree encoded in its material form, is a reasonable image to describe what has taken place. The tree does not magically appear out of a dead, material form; rather there is a complex genetic map that is built into the seed, and when planted and given proper conditions, this genetic coding begins to act and gathers Matter and infuses life-energy to create the eventual tree.
Man is recognized as “the mental being” because of the obvious capacities of the mind that are evident in humanity, and the results that eventuate with human beings systematically reshaping the material and vital existence of the world. The involution of mind into the material world, and its subsequent evolution and expression, shows both the preexistence of mind and what we may call a “mental world” in the formation of existence as we know it. This is consistent with the idea that the Brahman creates the entire universe out of His own substance, according to His own plan of development, with the progression from Sat-Chit-Ananda through the supramental level that maintains its awareness and oneness with Sat-Chit-Ananda while creating the multifarious forms and forces that make up the play of life in the world, encompassing the actions of mind, life and matter.
Those who follow a spiritual aspiration, who practice a form of Yoga, or who are dedicated to a religious life of self-examination find that there is a secret heart wherein resides the Self, the Immanent Divine. Through connection with that Self, they identify with and unify the being with the Divine Presence.
Sri Aurobindo, The Upanishads, Mundaka Upanishad, pp. 193-210