The 10th mantra of the dwitiya valli of the prathama adhyaya of Kathopanishad -
जानाम्यहं शेवधिरित्यनित्यं न ह्यध्रुवैः प्राप्यते हि ध्रुवं तत् ।
ततो मया नाचिकेतश्चितोऽग्निः अनित्यैर्द्रव्यैः प्राप्तवानस्मि नित्यम् ॥
O Nachiketas! The worldly objects, which are called treasures (Shevadhis), I have understood to be impermanent. The eternal (Dhruva) cannot, by any means, be attained through impermanent (Adhruva) things. Therefore, I have chosen the sacred fire named Nachiketa Agni. In this way, I have been able to attain the eternal essence amidst impermanent things.
Nachiketa Agni is explained in - https://www.vedadhara.com/yamaraja-teaches-nachiketas-about-the-two-types-of-yajnas
Yamaraja emphasizes that material possessions, often regarded as valuable treasures, are transient and do not lead to eternal fulfillment. True permanence or eternal truth cannot arise from things that are inherently temporary. By choosing the sacred fire (named after Nachiketas), Yamaraja aligns himself with eternal truth over fleeting material gains.
Worldly materials are temporary and thus referred to as 'mortal' or 'Mrityuroopa'. They appear valuable only as long as ignorance (Avidya) persists. Without knowledge, one cannot differentiate between the eternal (Amrit or Nitya) and the transient (Mrityu or Anitya). Once knowledge is attained, the understanding of this distinction becomes clear.
However, this does not mean that worldly objects have no role in attaining spiritual truth. The interpretation depends on one’s outlook and understanding. Worldly objects are both destructive and constructive. If one views them as ends in themselves and remains attached to them, they become a source of bondage. If one sees them as tools for spiritual progress, they become a means to liberation.
The same impermanent objects can either bind or liberate, based on whether they are seen as transient pleasures or as stepping stones to eternal truth. The eternal is hidden within the transient, and the wise learn to access it. Yamaraja advises humans to focus on the eternal essence within the transient material world, as it is through such discernment that liberation is achieved. He emphasizes that one need not seek spiritual truth outside the material world; it is hidden within worldly objects themselves.
All Yajnas produce temporary results, except for the Chayana Yajna, which leads to the realization of the eternal.
'Bhooteshu bhooteshu vichitya dheeraah, pretyaasmaallokaadamritaah bhavanti' from Kenopanishad also reinforces the idea that the eternal (Amrita) is present in all worldly objects. Wisdom lies in recognizing this eternal essence and striving to attain it.