Lets see what we learn from the fourth upanishad.
“Man is composed of such elements as vital breath, deeds, thought, and the senses – all of them deriving their being from the Self. They have come out of the Self, and in the Self they ultimately disappear – even as the waters of a river disappear in the sea.”
At the beginning of Prasna, the fourth upanishad that we are studying, we are introduced to some seekers of truth: “Sukesha, Satyakama, Gargya, Kousalya, Bhargava, and Kabandi, devotees and seekers after the truth of the supreme Brahman, with faith and humility approached the sage Pippalada. Said the sage: Practice austerity, continence, faith for a year; then ask what questions you wish. If can, I will answer.
After a year Kabandi approached the teacher and asked: ‘Sir, how did the creatures come into being?’ ‘The Lord of beings,’ replied the sage, ‘meditated and produced Prana, the primal energy, and Rayi, the giver of form, desiring that they, male and female, should in manifold ways produce creatures for him. Prana, the primal energy, is the sun; and Rayi, the form-giving substance is the moon…The rising sun pervades the east, and fills with energy all beings that there inhabit; and likewise when his rays fall on the south, the west, the north, the zenith, the nadir, and the intermediate regions, to all beings that there inhabit he gives life. Prana is the soul of the universe…'”