Katha-1-1-26-śvobhāvā

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

Though thus tempted, Nachikêtas unagitated like a large lake, said: svôbhâvah, enjoyments whose existence the next day is a matter of doubt; the enjoyments enumerated by you are ephemeral; again. Oh Death, they tend to the decline of the vigour of all the organs of man. These nymphs and other enjoyments only tend to harm, because they destroy virtue, strength, intellect, vigour, fame and the rest. As for the longevity that you will give me, hear me on that point. All life, even that of Brahma is, indeed, short. What need be said of our longevity. Therefore, keep the chariots, etc., for thyself alone, as also the dance and music.

Links
Various resources on the Kathopanishad
Upanishad Series – Katopanishad Commentary by Swami Chinmayananda