Śvetāśvatara Upaniṣad · 1..13

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 dweller in all —the witness, the presider, free from qualities. He who sees Him, sees the Ātman, not another.

The deva (shining God) is not in a distant heaven but gūḍha (hidden) in every being, as oil in the seed or butter in milk. He is sarvavyāpī (all-pervading), not as water soaks a sponge, but as consciousness animates the body. The key phrase: he who sees Him, sees the Ātman, not “another” —because there is no other. In our yoga practice, when we stop seeking external mystical experiences and recognize the Witness in ourselves and in all others, separation dissolves. He is nirvikāra (without modifications), the immutable constant amidst all change.