The Puruṣa of the size of a thumb, luminous like a flame without smoke, the lord of past and future — He himself is today and He is tomorrow. This is in truth That.

This verse continues the description of the Ātman as pure light.

Aṅguṣṭhamātraḥ puruṣaḥ — the Puruṣa of thumb’s size. The subtle dimension of being.

Jyotir ivādhūmakaḥ — luminous like a flame without smoke. Pure light, without darkness or impurity.

Īśāno bhūtabhavyasya — the lord of past and future.

Sa evādya sa u śvaḥ — He himself is today and He is tomorrow. The eternal present.

Etad vai tat — this is in truth That.

The smokeless flame (jyoḥr adhūmaka) symbolizes pure consciousness, without the darkness of ignorance.