BhG 8.21

syntax

avyaktaḥ (unmanifested) akṣaraḥ iti (imperishable) uktaḥ (is called),
tam (that) paramām gatim (supreme goal) āhuḥ (they declared).
yam (that which) prāpya (after obtaining) na nivartante (they do not return),
tat (that) mama (my) paramam dhāma (supreme abode) [asti] (it is).

grammar

avyaktaḥ	–	a-vyakta (vi-√añj – to decorate, to make visible) PP 1n.1 m. – unmanifested, invisible, unevolved;
akṣaraḥ	–	a-kṣara 1n.1 m. – imperishable, a syllable (from: √kṣar – to flow, to perish, kṣara – perishable);
iti	–	av. – thus (used to close the quotation);
uktaḥ	–	ukta (√vac – to speak) PP 1n.1 m. – is said, called;
tam	–	tat sn. 2n.1 m. – that;
āhuḥ	–	√ah (to speak – inflected only in Perf., other forms from: √brū) Perf. P 1v.3 – they spoke, they declared;
paramām	–	paramā 2n.1 f. –  supreme, the highest (superlative of: para – beyond, ancient, final, the best, the supreme);
gatim	–	gati 2n.1 f. – moving, passage, means, refuge, goal (from: √gam – to go);
yam	–	yat sn. 2n.1 m. – that which;
prāpya	–	pra-√āp (to obtain) absol. – after obtaining;
na	–	av. – not;
nivartante	–	ni-√vṛt (to stop, to turn back) Praes. Ā 1v.3 – they return;
tat	–	tat sn. 1n.1 n. – that;
dhāma	–	dhāman 1n.1 n. – abode, house, state, majesty, splendour (from: √dhā – to put);
paramam	–	parama 1n.1 n. – supreme, the highest (superlative of: para – beyond, ancient, final, the best, the supreme);
mama	–	asmat sn. 6n.1 – my;

textual variants

yaṁ → yat / yaḥ (which / he who);
nivartante → nivarteta (he would not return);

The third and fourth pada of verse 8.21 are almost the same as the third and fourth pada of verse BhG 15.6 (the last pada relates to the fourth pada of: Kaṭhopaniṣad 3.9);

Śāṃkara

yo’sāv avyakto’kṣara ity uktas tam evākṣara-saṃjñakam avyaktaṃ bhāvam āhuḥ paramāṃ prakṛṣṭāṃ gatim | yaṃ paraṃ bhāvaṃ prāpya gatvā na nivartante saṃsārāya, tad dhāma sthānaṃ paramaṃ prakṛṣṭaṃ mama, viṣṇoḥ paramaṃ padam ity arthaḥ

Rāmānuja

atha kaivalyaṃ praptānām api punarāvṛttir na vidyata ity aha

tasmād avyaktād acetanaprakṛtirūpāt puruṣārthatayā paraḥ utkṛṣṭo bhāvo ‚nyo jñānaikākāratayā tasmād visajātīyaḥ, avyaktaḥ kenacit pramāṇena na vyajyata ity avyaktaḥ, svasaṃvedyasvāsādhāraṇākāra ityarthaḥ; sanātanaḥ utpattivināśānarhatayā nityaḥ yaḥ sarveṣu viyadādibhūteṣu sakāraṇeṣu sakāryeṣu vinaśyatsu tatra tatra sthito ‚pi na vinaśyati; saḥ avyakto ‚kṣara ityuktaḥ, „ye tv akṣaram anirdeśyam avyaktaṃ paryupāsate”, „kūṭastho ‚kṣara ucyate” ityādiṣu taṃ vedavidaḥ paramāṃ gatim āhuḥ / ayam eva, „yaḥ prayāti tyajan dehaṃ sa yāti paramāṃ gatim” ity atra paramagatiśabdanirdiṣṭo ‚kṣaraḥ prakṛtisaṃsargaviyuktasvasvarūpeṇāvasthita ātmetyarthaḥ / yam evaṃbhūtaṃ svarūpeṇāvasthitaṃ prāpya na nivartante; tan mama paramaṃ dhāma paraṃ niyamanasthānam / acetanaprakṛtir ekaṃ niyamanasthānam; tatsaṃsṛṣṭarūpā jīvaprakṛtir dvitīyaṃ niyamanasthānam / acitsaṃsargaviyuktaṃ svarūeṇāvathitaṃ muktasvarūpaṃ paramaṃ niyamanasthānam ityarthaḥ / tac cāpunarāvṛttirūpam / atha vā prakāśavācī dhāmaśabdaḥ; prakāśaḥ ceha jñānam abhipretam; prakṛtisaṃsṛṣṭāt parichinnajñānarūpād ātmano ‚paricchinnajñānarūpatayā muktasvarūpaṃ paraṃ dhāma

Śrīdhara

avināśe pramāṇaṃ darśayann āha avyakta iti | yo bhāvo ‚vyakto ‚tīndriyaḥ | akṣaraḥ praveśa-nāśa-śūnya iti | tathākṣarāt saṃbhavatīha viśvaṃ ity ādi-śrutiṣv akṣara ity uktaḥ | taṃ paramāṃ gatiṃ gamyaṃ puruṣārtham āhuḥ | puruṣān na paraṃ kiṃcit sā kāṣṭhā sā parā gatiḥ ity-ādi-śrutayaḥ | parama-gatitvam evāha yaṃ prāpya na nivartanta iti | tac ca mamaiva dhāma svarūpam | mamety upacāre ṣaṣṭhī | rāhoḥ śira itivat | ato ‚ham eva paramā gatir ity arthaḥ

Madhusūdana

yo bhāva ihāvyakta ity akṣara iti cokto ‚nyatrāpi śrutiṣu smṛtiṣu ca taṃ bhāvam āhuḥ śrutayaḥ smṛtayaś ca puruṣān na paraṃ kiṃcit sā kāṣṭhā paramā gatiḥ ity ādyāḥ | paramām utpatti-vināśa-śūnya-sva-prakāśa-paramānanda-rūpāṃ gatiṃ puruṣārtha-viśrāntim | yaṃ bhāvaṃ prāpya na punar nivartante saṃsārāya tad-dhāma svarūpaṃ mama viṣṇoḥ paramaṃ sarvotkṛṣṭam | mama dhāmeti rāhoḥ śira itivad bheda-kalpanayā ṣaṣṭhī | ato ‚ham eva paramā gatir ity arthaḥ

Viśvanātha

pūrvokta-ślokoktam avyakta-śabdaṃ vyācaṣṭe avyakta iti | na kṣaratīty akṣaro nārāyaṇaḥ eko nārāyaṇa āsīn na brahmā na ca śaṅkaraḥ iti śruteḥ | mama paramaṃ dhāma nityaṃ svarūpam | yad vā akṣaraḥ paraṃ dhāma brahmaiva mad-dhāma mat-tejo-rūpam

Baladeva

yo bhāvo mayehāvyakta ity akṣara iti cocyate taṃ vedāntāḥ paramāṃ gatim āhuḥ puruṣān na paraṃ kiṃcit sā kāṣṭhā paramā gatiḥ ity ādau | yaṃ bhāvaṃ prāpyopetya janāḥ punar na nivartante janma nāpnuvanti sa bhāvo ‚ham evety āha tad iti | tan mamaiva dhāma svarūpaṃ paramaṃ śrīmat ṣaṣṭhīyaṃ caitanyam ātmanaḥ svarūpam itivad avagantavyā