34. Katha Upanishad

Discussion on verse 3.12 3.12 eṣaḥ sarveṣu bhūteṣu gūḍhaḥ ātmā na prakāśate । dṛśyate tu agryayā buddhyā sūkṣmayā sūkṣma-darśibhiḥ ॥ This Self, hidden in all beings, does not reveal itself easily. Yet it is perceived by subtle seers through a sharp and refined intellect.