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.
On "the knowledge of Brahman," given by grace: an examination of the syllable Oṃ, the structure of the subtle body, and the path of breath. It ends with the knower being called Puruṣa — a Person, not an impersonal principle.