Sri Aurobindo translates Katha Upanishad, Second Cycle: First Chapter, Verses 10-11: “What is in this world, is also in the other: and what is in the other, that again is in this: who thinks he sees difference here, from death to death he goes. Through the mind must we understand that there is nothing in this world that really varies: who thinks he sees difference here, from death to death he goes.”
These verses highlight the unity of the entire creation. The mind tends to see fragmentation, division and separation — it focuses on differentiation through its analytical processes. This is a matter of the focus of attention. The mind also has the capability of moving beyond division to unity, through the processes of meditation and yoga. As the mind becomes quiet, it becomes capable of experiencing the unity of the manifestation; it can see the inter-connectedness of all and the common substrate of everything that exists.
The quieting of the mind also prepares the being for the shift of standpoint from the individual egoistic view to the divine unified view. The cycle of birth and death is relevant in the world of forms and the separate view of life, but loses its relevance in a unified view that sees the constant change as a process of manifestation of one being, taking on and discarding specific forms, while remaining One at all times.
Sri Aurobindo, The Upanishads, Katha Upanishad, pp. 213-241, and Kapali Sastry, Lights on the Upanishads, pp. 104-129