Yat tat — that which — agre — at the start — visham iva — like poison; parinaame — at maturation — amrita-upamam — like nectar. Tat sukham sattvikam proktam — that is declared sattvika happiness. Atma-buddhi-prasada-jam — born from the clarification of buddhi turned toward atman.
Krishna names sattvika sukha by its temporal signature: bitter-then-sweet. The discipline that produces it is initially poison-like; matured, it is nectar-like.
Shankara reads sattvika joy as arising from the clarified atma-buddhi turned toward the Self — like pure water cleared of sediment. At the outset of jnana, vairagya, samadhi-practice it presents as bitter as poison, for it demands extreme effort against the grain of habit. At maturation it is like amrita, for it is nothing other than the Self's own luminosity recognized as Self. The temporal pattern is the chapter's sattvika-sukha-diagnostic: discipline-first, joy-later.
Madhusudana identifies this joy precisely as samadhi-sukha. It appears at the outset as dvesha-vishesha-avaha — aversion-inducing, like poison — because the entire weight of effort in jnana, vairagya, dhyana must be borne before the taste arrives. At maturation it becomes the seat of supreme love — priti-atishaya-aspada — nectar. The verse holds the bhakti-jnani's whole sadhana-arc in one image.
Ramanuja reads sattvika joy emerging when the buddhi, withdrawn from all other objects, rests solely on the distinct atman's nature. At yoga-practice's commencement this joy is like poison — onerous, unfamiliar, the distinct self not yet disclosed. When practice matures and the self's svarupa becomes manifest, that joy becomes amrita-upama. The bhakta's practice is the bridge from poison-taste to nectar-taste.
Madhva reads sattvika joy as ata-buddhi-prasada-jam — arising from the clarification of the jiva's buddhi directed toward its real nature. In dvaita that nature is paratantra; the buddhi clarified is the buddhi that has correctly recognized the jiva's eternal subordination to svatantra Hari. The poison-then-nectar pattern: initially the recognition feels like loss of self-claim; matured, it reveals as the only joy that lasts.
Vallabha identifies this joy with the self's own svarupa-avirbhava — the arising of one's true form into experience. At yoga-practice's commencement the aspirant lacks experience of the distinct atman-nature, so what presents itself is painful. At paripaka — maturation — the svarupa emerges into felt reality and that is amrita. Pushti-marga: prasada brings the avirbhava; the bhakta's practice is preparation for grace's revealing of svarupa.
Shridhara reads sattvika sukha as that which arises when atma-buddhi achieves prasada — clarity through shedding the impurities of rajas and tamas. At the outset onerous because dependent on manas-samyama; seems like poison. At maturation, when the buddhi has settled in its own clarity, the joy becomes amrita-upama. The chapter's most precise temporal-pattern of true sukha is delivered.