Sri Aurobindo translates Katha Upanishad, Second Cycle: First Chapter, Verses 6-9: “He is the seer that sees Him who came into being before austerity and was before the waters: deep in the heart of the creature he sees Him, for there He stands by mingling of the elements. This is That thou seekest. This is Aditi, the mother of the Gods, who was born through the Prana and by the mingling of the elements had her being: deep in the heart of things she has entered, there she is seated. This is That thou seekest. As a woman carries with care the unborn child in her womb, so is the Master of Knowledge lodged in the tinders: and day by day should men worship Him, who live the waking life and stand before Him with sacrifices; for He is that Agni. This is That thou seekest. He from whom the sun arises and to whom the sun returns, and in Him are all the Gods established; none passes beyond Him. This is That thou seekest.”
The term translated here as austerity is tapas. Elsewhere Sri Aurobindo has translated the term as “concentration of conscious force”, which is the essential meaning of austerity. It is good to keep this in mind. The creation of the universe, the manifestation of forms, forces and beings, all takes place through the concentration of conscious force of the supreme Brahman. Brahman exists beyond the limits of created forms, pervades, permeates and acts as the ground of being for everything that is, both the unmanifest and the manifest. The elements referred to here are the five elements of the creation, earth, water, fire, air and ether.
These verses describe the nature of the Brahman as first cause and sole existent in an omnipresent reality.
Sri Aurobindo, The Upanishads, Katha Upanishad, pp. 213-241, and Kapali Sastry, Lights on the Upanishads, pp. 104-129