Katha-2-2-15-na tatra

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

The reply here is that it shines and is perceived as shining. The sun, though the enlightener of all, does not shine in the Brahman, being his âtman, i.e., the sun does not illumine the Brahman. Similarly, the moon and the stars do not; nor do these lightnings illumine. How could this fire, perceivable by us? Why say much? All these, the sun and the rest who shine, shine only after him, the lord of all; as water, firebrand, etc., from their contact with fire, burn after the burning fire and not by their own inherent virtue. It is by his light only, that all this, the sun and the rest shine. This being so, that Brahman alone shines and shines variously. From the various kinds of light possessed by its effects, the self-luminosity of the Brahman is inferred. It is not possible for one to impart to another luminosity, which one does not possess, because pots, etc., are found incapable of illumining other objects and the sun and the rest, luminous in their nature, are found capable of that.

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॥ इति काठकोपनिषदि द्वितीयाध्याये द्वितीया वल्ली ॥

|| iti kāṭhakopaniṣadi dvitīyādhyāye dvitīyā vallī ||

Here ends the Fifth Part.

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