Sri Aurobindo translates Prashna Upanishad, first question, verses 6 – 8: “Now when the Sun rising entereth the East, then absorbeth he the eastern breaths into his rays. But when he illumineth the south and west and north, and below and above and all the angles of space, yea, all that is, then he taketh all the breaths into his rays. Therefore is this fire that riseth, this Universal Male, of whom all things are the bodies, Prana the breath of existence. This is that which was said in the Rig Veda: ‘Fire is this burning and radiant Sun, he is the One lustre and all-knowing Light, he is the highest heaven of spirits. With a thousand rays he burneth and existeth in a hundred existences: lo this Sun that riseth, he is the Life of all his creatures.’ ”
The Rishi takes a deeper look at the interplay of Matter and Energy. Energy is seen as the universal Prana, and it enlivens all bodies, that is, all Matter. We see this interplay in the energy of the sun as it brings forth all forms of life on the earth. It goes beyond this to the entire creation as a universal phenomenon.
There is also the esoteric symbolism that the Vedic Rishis used to communicate a secret inner sense to those they were teaching, while holding an external meaning for those without this further grounding in the practices being taught. Sri Aurobindo describes this use of dual meaning at length in The Secret of the Veda.
As the Isha Upanishad describes, the sun is the sun of illumination of knowledge, covered by a brilliant golden lid which, when the seeker pierces it, gives him access to the higher planes of knowledge, the Vijnana, as described in the Taittiriya Upanishad. Knowledge of the entire universal manifestation is lodged at this level, and in fact, this is the effective level that acts to transform the Oneness into the Multiplicity, which is the birth and “life of all his creatures.” This sun of illumination creates, directs, motivates and actualises all the life-force in the universe.
Sri Aurobindo, The Upanishads, Prashna Upanishad, pp.297-315