Bhagavad Gita · Sankhya YogaChapter 2, Shloka 29 (2.29)

The self — a wonder. Something never seen before, marvellous, appearing suddenly — such is the knowledge of the self (Shankaracharya: adṛṣṭapūrvam adbhutam). Knowing the self is not like knowing any other thing.

Two readings (Shankaracharya): (1) The self itself is like a wonder — someone sees, speaks of and hears of it as a wonder. (2) Or — the person who sees, speaks of or hears of the self is like a wonder — one in thousands. The conclusion of both: the self is hard to grasp.

Ramanuja's explanation: The self is a wonder because it is of an entirely different kind from all other things. Among countless beings, when sins have been worn away and merit increased through great austerity, some rare one sees it; some rare one like that tells others of it; some such one hears of it — and even after hearing, no one knows it in truth. By "ca" (and): even among those who see, speak and hear, seeing, speaking and hearing in truth is rare.

"Śrutvāpy enaṃ veda na caiva kaścit" — even after hearing, no one knows it. The humblest line: merely hearing is not enough. Knowledge must go beyond hearing — into experience and into life.

Connection with the Katha Upanishad: The Katha Upanishad (1.2.7) has a similar thought — "which many do not even get to hear of, which many, even hearing, do not know; wonderful is the one who teaches it…".