By which one perceives the end of sleep and the end of wakefulness — both states — knowing that great, omnipenetrating Ātman, the wise one does not grieve.

This verse describes the Ātman as the witness of all states of consciousness.

Svapnāntaṃ jāgaritāntaṃ ca — the end of sleep and the end of wakefulness. Refers to the states of sleep and waking.

Ubhau yenānupaśyati — both of which are perceived. The Ātman is the one who experiences and transcends both states.

Mahāntaṃ vibhum ātmānaṃ — the great, omnipenetrating Ātman. Mahat = great; Vibhu = omnipresent, that penetrates all.

Matvā dhīro na śocati — knowing, the wise one does not grieve. Knowledge of the Ātman liberates from suffering.

In yoga, the practice of sākṣī-bhāva (witness attitude) cultivates this vision of the Ātman that transcends the changes of consciousness states.