The Upaniṣads — the philosophical core of the Vedic tradition, revealing the nature of Brahman, the Ātman, knowledge, action and liberation. The ten principal Upaniṣads together with select minor Vaiṣṇava Upaniṣads.
The first half is Vaiṣṇava prose on the syllable Oṃ and on Viṣṇu; the second, verses on non-duality. The book's worth lies in how these two voices come together. It ends with a promise to one who "does not return again."