Sri Aurobindo translates Prashna Upanishad, Third Question, Verses 8-12: “The Sun is the main breath outside this body, for it cherisheth the eye in its rising. The divinity in the earth, she attracteth the lower breath of man, and the ether between is the medial breath: air is the breath pervasor. Light, the primal energy, is the upper breath: therefore when the light and heat in a man hath dwindled, his senses retire into the mind and with these he departeth into another birth. Whatsoever be the mind of a man, with that mind he seeketh refuge with the breath when he dieth, and the breath and the upper breath lead him with the Spirit within him to the world of his imaginings. The wise man that knoweth thus of the breath, his progeny wasteth not and he becometh immortal. Whereof this is the Scripture: By knowing the origin of the Breath, his coming and his staying and his lordship in the five provinces, likewise his relation to the Spirit, one stall taste immortality.”
The Upanishad here makes the correspondences between the universal and the individual, with respect to the operation of the Prana, the active energy of the universe. This links up the earlier discussion about the universal life-force and its detailed operations within the individual being, and now goes back to translate the fivefold primary functional subdivisions of Prana as operative in the body to their corresponding action in the universe. The “doctrine of signatures” identifies correspondences in Nature with functions in the human being. Thus the sun is seen as corresponding to the primary energy of Prana, through its initial activating force and its relation to the eye. Similarly, the Apana, the lower breath, corresponds to the earth-energy. Ether represents the functioning of the Samana. Air represents the energy we identify as the Vyana. Udana, which is the energy which moves the life-force from one existence through rebirth into another is identified with the force that takes up the Prana as it readies itself to depart the body.
The process involved then revolves around the focus, intensity and direction of the energy of the being which guides the life-force in its departure and subsequent taking up of a new form in a new life. The Atman has gathered various experiences and built an energetic unit that has momentum, what we generally call “karma” that shows the direction in which the Atman will next organize a body and line of action. The options of a world of virtue, a world of suffering, or a mixed world of human life combining both joy and suffering were covered in a prior segment of this Upanishad.
The soul who recognises these truths and identifies with the Atman, transcends the experience of an individual body or life, and thus, “tastes immortality.”
Sri Aurobindo, The Upanishads, Prashna Upanishad, pp.297-315