Māndukya 1.02

sarvaṁ hyetad brahma। ayamātmā brahma। so'yamātmā catuṣpāt ॥2॥

All this is indeed Brahman. "This Ātmān is Brahman". This self has four aspects.

Bhāshya 1.02

"All this is indeed Brahman" - indicates that fullness is that of Brahman, and no one else. To explain "This Ātmān is Brahman", a testimonial from Harivamsa is referenced where the utterances of Varuna in the form of a frog specifically explains Māndukyōpanishad. The text suggests that within all bodies, starting from the divine Brahman, there exists an entity perceived as the doer of actions. Observing the lack of independence among beings, it is demonstrated that this entity is indeed the Ātmān, which is Brahman.

"paramaṁ yo mahadbrahma", "tadeva brahma paramaṁ kavīnām", "pūrṇamadaḥ pūrṇam idam"

"The supreme entity, known as the great Brahman", "That is indeed the supreme Brahman revered by the sages", "That is whole, this is whole"

ityādiṣu prasiddhaṃ ca brahmaṇaḥ pūrṇatvamityāha – sarvaṃ hyetat brahmeti॥

- in such statements, it is well-known that fullness is of Brahman; thus it is said: "All this is indeed Brahman."

śrībrahmādisakaladeheṣu sthitvā''dānadikartā yo'yaṃ kaścit pratīyate। jīvānāṃ asvātantryadarśanāt so'pi sa eveti darśayati – ayamātmā brahmeti।

The text suggests that within all bodies, starting from the divine Brahman, there exists an entity perceived as the doer of actions. Observing the lack of independence among beings, it is demonstrated that this entity is indeed the Ātmān, which is Brahman.

"pūrṇastu harirevaiko nānyat pūrṇaṃ kadācana। vinā ca prakṛtiṃ nānyat kālātītaṃ parātmanaḥ॥

"Hari alone is complete; nothing else is ever complete. Without Prakrti, nothing else transcends time of the Supreme Ātmān.

kālaścaiva diśo vedāḥ prakṛtyātmāna īritāḥ। abhimānāttu jīvānāṃ na kālātītatā bhavet॥

Time, directions, and the Vedas are governed by the combination of Prakṛti and Ātmān. However, due to pride, living beings cannot transcend time.

muktānām api pūrvatra kālasambandha īritaḥ। pūrṇatvaṃ ca sadā viṣṇoḥ prasiddhaṃ sarvavedataḥ॥

Even for the liberated souls, the relationship with time is stated. The completeness and eternal nature of Lord Vishnu are well-known from all the Vedas.

so'yaṁ viṣṇū ramābrahmarudrānantādigaḥ sadā। ādānādanakartṛtvādātmā teṣāmagocaraḥ॥ iti maṇḍūkarūpī san dadarśa varuṇaḥ śrutim॥"

Thus, Lord Vishnu, who is always with goddess Lakshmi, Brahma, Rudra, Ananta, and others in the form of Ātmān, is beyond perception due to his giving and taking (as per their tendencies) and he himself being non-partisan in doership. In the form of a frog, Varuna discovered this Vedic knowledge."

iti harivaṃśeṣu ॥2॥

- stated thus in the Harivamsa.