The Puruṣa of the size of a thumb resides in the center of the Ātman, as the lord of past and future — he does not fear after that. This is in truth That.

This verse describes the Ātman in its subtle dimension within the heart.

Aṅguṣṭhamātraḥ puruṣaḥ — the Puruṣa of thumb’s size. A symbolic measure of the inner being.

Madhya ātmani tiṣṭhati — resides in the center of the Ātman. In the core of being.

Īśānaṃ bhūtabhavyasya — the lord of past and future. The controller of time.

Na tato vijugupsate — he does not fear after that. Knowledge of the Ātman liberates from fear.

Etad vai tat — this is in truth That.

In the practice of yoga, meditation on the Ātman of thumb’s size in the heart is an ancient technique to contact the inner divine dimension.