Śvetāśvatara Upaniṣad · 3..18

एको देवः सर्वभूतेषु गूढः सर्वव्यापी सर्वभूताधिवासः आत्मयोनिः स्वयंजातो निर्विकारो यः स पश्यति तदात्मनोऽन्यम्

eko devaḥ sarvabhūteṣu gūḍhaḥ sarvavyāpī sarvabhūtādhivāsaḥ ātmaśaktirnirvikāro yāḥ sa paśyati tadevānyat

The one God, hidden in all beings, all-pervading, the indweller of all —the witness, the presider, free from qualities. He who sees Him, sees the Ātman, not another.

This verse repeats 1.13, emphasizing its importance. The deva (shining god) is gūḍha (hidden) not because it is difficult to find, but because it is so close we overlook it. It is sarvavyāpī (all-pervading) like salt in water, indistinguishable but present in every part. In our yoga practice, when we develop vision of ātma-śakti (the power of being), we see there is no “other.” What appeared as multiplicity is unity; what appeared as separation is connection. To see antaryāmin in all is to see Ātman in all.