BhG 5.21

syntax

bāhya-sparśeṣu (in external perceptions) asaktātmā (whose self is unattached) ātmani (in the self) yat sukhaṁ (which pleasure) [tat] (that) vindati (he obtains).
saḥ (he) brahma-yoga-yuktātmā (whose self is engaged in yoga of brahman) akṣayam (indestructible) sukham (pleasure) aśnute (he attains).

grammar

bāhya-sparśeṣu	–	bāhya-sparśa 7n.3 m.; TP: bāhyeṣu sparśeṣv iti – in external perceptions (from: bahiḥ – av. outside, bāhya – external; √spṛś – to touch, sparśa – touch, sensation);
asaktātmā	–	asakta-ātman 1n.1 m.; BV: yasya ātmāsakto ‘sti saḥ – whose self is unattached (from: √sañj – to attach, to stick, to embrace, PP a-sakta – unattached; ātman – self);
vindati	–	√vid (to find) Praes. P 1v.1 – he finds, he obtains;
ātmani	–	ātman 7n.1 m. – in the self;
yat	–	yat sn. 2n.1 n. – that which;
sukham	–	sukha 2n.1 n. – pleasure, comfort (from: su – prefix: good, excellent, beautiful, virtuous; kha – cavity, hole, nave; su-kha – joy, happiness, literally: good hole in the nave [of a wheel through which an axis runs] that makes the moving smooth; or from: su-√sthā; opposite to: duḥkha – pain, difficulty);
saḥ	–	tat sn. 1n.1 m. – he;
brahma-yoga-yuktātmā	–	brahma-yoga-yuktātman 1n.1 m.; BV: yasyātmā brahmaṇo yoge yukto ‘sti saḥ – whose self is engaged in yoga of brahman (from: √bṛh – to increase, brahman – spirit, the Vedas; √yuj – to yoke, to join, to engage, yoga – yoga, yoking, application, a means, one of the schools of Hindu philosophy; PP yukta – yoked, endowed with; ātman – self); or: BV: yasyātmā brahmaṇi yogena yukto ‘sti saḥ – whose self is joined with brahman by yoga;
sukham	–	sukha 2n.1 n. – pleasure, comfort (from: su – prefix: good, excellent, beautiful, virtuous; kha – cavity, hole, nave; su-kha – joy, happiness, literally: good hole in the nave [of a wheel through which an axis runs] that makes the moving smooth; or from: su-√sthā; opposite to: duḥkha – pain, difficulty);
akṣayam	–	a-kṣaya 2n.1 n. – indestructible (from: √kṣi – to decrease, PF kṣaya – diminution, destruction);
aśnute	–	√aś (to reach, to eat, to enjoy) Praes. Ā 1v.1 – he attains;

textual variants

bāhya-sparśeṣv → brāhma-sparśeṣv / bāhu-sparśeṣv (in perceptions of brahman / in many perceptions);
yat → yaḥ (he who);
brahma-yoga-yuktātmā → brahma-loka-yuktātmā (whose self is joined with the world of brahman);
akṣayam → avyayam / akṣayyam (unchangeable / indestructible);

Śāṃkara

kiṃ ca, brahmaṇi sthitaḥ—

bāhya-sparśeṣu bāhyā ca te sparśāś ca bāhya-sparśāḥ | spṛśyante iti sparśāḥ śabdādayo viṣayās teṣu bāhya-sparśeṣu | asakta ātmā antaḥ-karaṇaṃ yasya so’yam asaktātmā viṣayeṣu prīti-varjitaḥ san vindati labhate | ātmani yat sukhaṃ tad vindatīty etat | sa brahma-yoga-yuktātmā brahmaṇi yogaḥ samādhir brahma-yogas tena brahma-yogena yuktaḥ samāhitas tasmin vyāpṛta ātmā antaḥ-karaṇaṃ yasya sa brahma-yoga-yuktātmā | sukham akṣayam aśnute vyāpnoti | tasmād bāhya-viṣaya-prīteḥ kṣaṇikāyā indriyāṇi nivartayed ātmany akṣaya-sukhārthīty arthaḥ

Rāmānuja

evamuktena prakāreṇa bāhyasparśeṣu ātmavyatiriktaviṣayānubhaveṣu, asaktātmā asaktamanāḥ antarātmany eva yaḥ sukhaṃ vindati labhate, sa prakṛtyabhyāsaṃ vihāya brahmayogayuktātmā brahmābhyāsayuktamanāḥ brahmānubhavarūpam akṣayaṃ sukhaṃ prāpnoti

Śrīdhara

moha-nivṛttyā buddhi-sthairye hetum āha bāhya-sparśeṣv iti | indriyaiḥ spṛśyanta iti sparśā viṣayāḥ | bāhyendriya-viṣayeṣv asaktātmānāsakta-cittaḥ | ātmani antaḥ-karaṇe yad upaśamātmakaṃ sāttvikaṃ sukham tad vindati labhate | sa copaśamaṃ sukhaṃ labdhvā brahmaṇi yogena samādhinā yuktas tadaikyaṃ prāpta ātmā yasya so ‚kṣayaṃ sukham aśnute prāpnoti

Madhusūdana

nanu bāhya-viṣaya-prīter aneka-janmānubhūtatvenātipracalatvāt tad-āsakta-cittasya katham alaukike brahmaṇi dṛṣṭa-sarva-sukha-rahite sthitiḥ syāt | paramānanda-rūpatvād iti cet, na | tad-ānandasyānanubhūta-caratvena citta-sthiti-hetutvābhāvāt | tad uktaṃ vārttike –

apy ānandaḥ śrutaḥ sākṣān mānenāviṣayīkṛtaḥ |
dṛṣṭānandābhilāṣaṃ sa na mandīkartum apy alam || iti |

tatrāha bāhyeti | indriyaiḥ spṛśyanta iti sparśāḥ śabdādayaḥ | te ca bāhyā anātma-dharmatvāt | teṣv asaktātmānāsakta-cittas tṛṣṇā-śūnyatayā viraktaḥ sann ātmani antaḥ-karaṇa eva bāhya-viṣaya-nirapekṣaṃ yad upaśamātmakaṃ sukhaṃ tad vindati labhate nirmala-sattva-vṛttyā | tad uktaṃ bhārate –

yac ca kāma-sukhaṃ loke yac ca divyaṃ mahat sukham |
tṛṣṇākṣaya-sukhasyaite nārhataḥ ṣoḍaśīṃ kalām || iti |

athavā pratyag-ātmani tvaṃ-padārthe yat sukhaṃ svarūpa-bhūtaṃ suṣuptāv anubhūyamānaṃ bāhya-viṣayāsakti-pratibandhād alambhamānaṃ tad eva tad-abhāvāl labhate |

na kevalaṃ tvaṃ-padārtha-sukham eva labhate kintu tat-padārthaikyānubhavena pūrṇa-sukham apīty āha sa tṛṣṇā-śūnyo brahmaṇi paramātmani yogaḥ samādhis tena yuktas tasmin vyāpṛta ātmāntaḥ-karaṇaṃ yasya sa brahma-yoga-yuktātmā | athavā brahmaṇi tat-padārthe yogena vākyārthānubhava-rūpeṇa samādhinā yukta aikyaṃ prāpta ātmā tvaṃ-padārtha-svarūpaṃ yasya sa tathā | sukham akṣayam anantaṃ sva-svarūpa-bhūtam aśnute vyāpnoti sukhānubhava-rūpa eva sarvadā bhavatīty arthaḥ | nitye ‚pi vastuny avidyānivṛtty-abhiprāyeṇa dhātv-artha-yoga aupacārikaḥ | tasmād ātmany akṣaya-sukhānubhavārthī san bāhya-viṣaya-prīteḥ kṣaṇikāyā mahā-narakānubandhinyāḥ sakāśād indriyāṇi nivartayet tāvataiva ca brahmaṇi sthitir bhavatīty abhiprāyaḥ

Viśvanātha

sa ca bāhya-sparśeṣu viṣaya-sukheṣv asaktātmā anāsakta-manāḥ | tatra hetur ātmani jīvātmani paramātmānaṃ vindati sati prāpte yat sukhaṃ tad akṣayaṃ sukham | sa evāśnute prāpnoti, na hi nirantaram amṛtāsvādine mṛttikā rocata iti bhāvaḥ

Baladeva

paurvauttaryeṇa sva-parātmānāv anubhavatīty āha bāhyeti | bāhya-sparśeṣu śabdādi-viṣayānubhaveṣu asaktātmā san yadātmani sva-svarūpe ‚nubhūyamāne sukham tadādau vindati, tad uttaraṃ brahmaṇi paramātmani yogaḥ samādhis tad-yuktātmā san yad akṣayaṃ mahad-anubhava-lakṣaṇaṃ sukham tad aśnute labhate