When one sees bhuta-prithak-bhava — the manifold differentiation of beings — as ekastham — resting in one ground; and from that very ground sees vistaram — the diffusion of variety — then he becomes Brahman, brahma sampadyate.
Krishna names the move from variety to unity to consummation: see all the multiplicity in one ground, see the spread also from that ground, and you become what you have been seeing.
Shankara reads precisely. When the seer perceives the manifold differentiation of beings as rooted in a single ground, and recognizes that all apparent multiplicity expands from that one source alone, action is seen to belong entirely to prakriti in its triple-guarded transformations, never to the atman. The atman is akarta, devoid of all linkage to action. Brahma sampadyate — becoming Brahman — is the dissolution of the false self-locus into the only locus that ever was.
Madhusudana addresses a subtle objection: if different atmans in different bodies act differently and enjoy differing fruits, how can seeing the atman as one in all beings be said not to harm oneself? The resolution: actions of speech, mind, and body in all their variety are performed by prakriti — the tri-gunatmika maya of the Lord, transformed into the mass of body and senses. The atman, equal across all, is never the doer. Brahma sampadyate is the jnani's full recovery into what he has always been.
Ramanuja reads with characteristic warmth: when the aspirant sees the manifold distinctions among beings — divinity, humanity, smallness, tallness — as residing in one substrate, and recognizes that this substrate is prakriti, the prakara of Brahman and not atman, then the diffusion of all further diversity — putra-pautra-adi-bheda-vistara — is likewise seen as proceeding from prakriti alone. At that point the seeker attains the atman freed from the field-confusion, in unobstructed relation with Bhagavan.
Madhva reads on the bheda-frame: true seeing is precisely this — the jiva perceives the atman as akarta. All differentiated states of beings are lent their appearance of agency by prakriti alone, while the atman — permanently distinct from prakriti and from svatantra Hari — bears no authorship of any act. The brahma-sampatti is the jiva's reaching unobstructed alignment with Hari, not merging into Him.
Vallabha reads the fruit of right self-seeing: all actions are indeed performed by prakriti alone in the Sankhya analysis, since kartritva attaches to activity and rests with prakriti, not with the chid-anu-atman, the infinitesimal conscious self. Yet that very atman is permeated by an unbroken thread of Purushottama-amsha-bhava — continuity with the supreme. Brahma sampadyate is the recognition of this amsha-relation, not the dissolution of the relation.
Shridhara reads through the standard objection: if beings visibly differ in virtuous and sinful actions, how can the atman be sama across them all? The answer: all actions of every kind are performed by prakriti in its transformations as body and senses — not by the atman from its own nature. The 'I act' arises from deha-abhimana, not from the atman's structure.