Oṃ — this syllable is all this. Its explanation: all that was, is, and will be is Oṃkāra. And what lies beyond the triple time — that too is only Oṃkāra.

The opening verse of the Māṇḍūkya Upaniṣad, the briefest but perhaps the most dense of all Upaniṣads.

Oṃ ity etad akṣaram — Oṃ, this syllable (akṣara = imperishable, syllable).

Idaṃ sarvam — is all this. The totality of existence.

The Oṃkāra encompasses:

• Bhūtam — what was (past)
• Bhavat — what is (present)
• Bhaviṣyat — what will be (future)

And more still:

• Trikālātītam — what lies beyond the triple time

Sarvaṃ oṃkāra eva — all is only Oṃkāra.

This Upaniṣad will develop how the three letters of Oṃ (A-U-M) correspond to the three states of consciousness (waking, dreaming, deep sleep), and the silence after Oṃ to the fourth state (turīya).

This verse establishes that Oṃ is not just a sacred sound but the symbol of Brahman itself.