This is the second of the four Mahāvākyas — the great sentences of the Upanishads. The Bṛhadāraṇyaka places it at the moment of creation: Brahman, in the beginning, knew only itself. And the knowing was this: I am Brahman.
The Upaniṣad then says: whoever among the gods recognised this — became Brahman. Whoever among the sages recognised this — became Brahman. And whoever among humans recognises this — becomes Brahman. The recognition is not a belief you adopt. It is not information you receive. It is the same recognition Brahman had of itself, occurring in you.
This is why Śaṅkarācārya says: liberation is not something that happens in the future, as a result of practice. It is the recognition of what is already the case. Aham brahmāsmi — I am Brahman — is not a claim to be argued for. It is the ground of all arguing, all knowing, all being.
Layer 3 — What it points toThe passage appears in the context of Brahman's primordial self-reflection before creation. The Sanskrit compound aham brahmāsmi joins aham (I) and asmi (am) with brahma in the nominative. The copula asmi asserts identity, not predication. It is not: I have the property of being Brahman. It is: I and Brahman are one and the same thing.
Śaṅkara's distinction between the two senses of aham is essential here. The empirical ego — the person with a name, memories, desires — is not Brahman. The recognition is not ego-inflation. What is Brahman is the witnessing awareness (sākṣin) that lies beneath the ego — the pure cit (consciousness) by which the ego itself is known. The instruction is to look past the ego to the witness, and recognise the witness as Brahman.
Layer 3 — What it points toThe Bṛhadāraṇyaka's framing of Aham Brahmāsmi within cosmogony is philosophically significant. Brahman's first act — if it can be called an act — is self-recognition. The world of multiplicity arises from that self-recognition (sṛṣṭi). And the liberation of the individual is the reversal of that movement: self-recognition occurring again, this time in the embodied individual. Śaṅkara in his bhāṣya on 1.4.10 emphasises that the passage identifies the cosmos and the individual self as two expressions of the same recognition — Brahman knowing itself as Brahman. The teacher's function (and the function of the Mahāvākya itself) is to occasion this recognition in the student.
The line 'becomes all this' (sarvam bhavati) is important: recognition of Brahman does not produce a new state or a special experience. It is the recognition that the knower was always the totality. Not a gain of something new but the fall of a false limitation.
Layer 3 — What it points to