This is indeed That.

This is one of the briefest and most dense verses in the entire Upaniṣad. With only four Sanskrit words, it encapsulates the essential teaching of Vedānta. Etat (this — the manifested, the immediate) vai (indeed, truly, certainly) tat (that — the absolute, the transcendent).

The identification between “this” and “that” is the heart of the non-dual vision (advaita). What appears as the multiplicity of objects in the world is in truth the single reality of Brahman. The appearance of separation is mithyā (apparent), not real in the absolute sense.

The verse can be interpreted in two complementary ways: (1) Yama is indicating that all things enumerated previously (elements, states of consciousness, etc.) are manifestations of Brahman; or (2) he is implicitly recognizing that Naciketas’s perseverance reveals the identity between the seeker and the sought.

The particle vai is emphatic — “truly, really, certainly.” It is not a tentative affirmation but the most direct expression of identity between the apparent and the real. This identity is tattva (the “that-ness,” the true nature of things).

In the Kaṭha Upaniṣad tradition, this verse serves as a bridge between Yama’s attempt to offer compensations and his eventual capitulation to Naciketas’s demand. Yama has tried all possible arguments and must finally recognize the truth: only knowledge of the Ātman satisfies.