BhG 2.55

syntax

śrī-bhagavān (the glorious Lord) uvāca (he spoke):
he pārtha (O son of Pṛthā!),
yadā (when) ātmanā (by the self) ātmani eva (in the self only) tuṣṭaḥ (satisfied) [san] (being) sarvān (all) mano-gatān (these which exist in the mind) kāmān (desires) prajahāti (he abandons),
tadā (then) sthita-prajñaḥ (one who has a firm wisdom) ucyate (it is called).

grammar

śrī-bhagavān	–	śrī-bhagavant 1n.1 m.; TP: śriyā yukto bhagavān iti – the Lord united with majesty (from: śrī – lustre, majesty, fortune; √bhaj – to share, to love, to rejoice, to worship, bhaga – a share, good fortune, opulence; bhagavant – who possesses opulence, -mant / -vant – suffix denoting one who possesses);
uvāca	–	√vac (to speak) Perf. P 1v.1 – he spoke;
prajahāti	–	pra-√hā (to leave, to abandon) Praes. P 1v.1 – he abandons;
yadā	–	av. – when (correlative of: tadā – at that time, then);
kāmān	–	kāma 2n.3 m. – wishes, desires, pleasures (from: √kam – to wish, to love, to long for);
sarvān	–	sarva sn. 2n.3 m. – all;
pārtha	–	pārtha 8n.1 m. – O son of Pṛthā (from: √pṛth – to extend, pṛthā – Kuntī, mother of the sons of Pāṇḍu);
mano-gatān	–	mano-gata 2n.3 m.; TP: manasi gatān iti – which are gone to the mind, exist in the mind (from: √man – to think, manas – the mind; √gam – to go, PP gata – gone);
ātmani	–	ātman 7n.1 m. – in the self;
eva	–	av. – certainly, just, merely;
ātmanā	–	ātman 3n.1 m. – by the self;
tuṣṭaḥ	–	tuṣṭa (√tuṣ – to become calm, to be satisfied) PP 1n.1 m. – calm, satisfied, pleased;
sthita-prajñaḥ	–	sthita-prajña 1n.1 m.; BV: yasya prajñā sthitāsti saḥ – one whose wisdom is firm (from: √sthā – to stand, PP sthita – standing, situated, firm; pra-√jñā – to know, to understand, to discern, prajñā – discrimination, wisdom, judgement);
tadā	–	av. – at that time, then;
ucyate	–	√vac (to speak) Praes. pass. 1v.1 – it is said;

textual variants

śrī-bhagavān → śrī-kṛṣṇa / bhagavān (the glorious Kṛṣṇa / the Lord);
mano-gatān → mano-harān (those which have stolen the mind);
tuṣṭaḥ → tuṣṭiḥ (satisfaction);
sthita-prajñas → sthira-prajñas / sthitaḥ prajñas (one who has fixed wisdom / steady, wise);
tadocyate → tathocyate (thus it is called);

Śāṃkara

The key:
an excerpt from the commented verse
quotes from the scriptures
starting polemic

From 2.55 to the end of the Discourse (adhyaya), the characteristic attributes of a man of steady knowledge as well as the means of obtaining that knowledge are taught to him who, having from the very commencement renounced all works, has entered upon a course of Devotion to Knowledge (jñāna-yoga-niṣṭha), as well as to him who has reached that stage by means of Devotion to works (Karma-yoga).		yo hy ādita eva saṃnyasya karmāṇi jñāna-yoga-niṣṭhāyāṃ pravṛttaḥ, yaś ca karma-yogena, tayoḥ prajahāti ity ārabhya adhyāya-parisamāpti-paryantaṁ sthita-prajña-lakṣaṇaṃ sādhanaṃ copadiśyate |
For, everywhere in spiritual science (adhyātma-śastra), the very characteristic attributes of the successful Yogin are taught as the means (of attaining that stage), since they are to be attained by effort. The Lord now points out those characteristic attributes which, as attainable by effort, constitute the means as well. (1) Satisfaction in the Self.		sarvatraiva hi adhyātma-śāstre kṛtārtha-lakṣaṇāni yāni tāny eva sādhanāni upadiśyante, yatna-sādhyatvāt | yāni yatna-sādhyāni sādhanāni lakṣaṇāni ca bhavanti tāni
The Lord said: When a man, satisfied in the Self alone by himself, completely casts off all the desires of the mind, then is he said to be one of steady knowledge.		śrī-bhagavān uvāca prajahāti yadā kāmān sarvān pārtha mano-gatān | ātmany evātmanā tuṣṭaḥ sthita-prajñas tadocyate ||2.55||
When a man completely abandons all the various desires that enter the heart		prajahāti prakarṣeṇa jahāti parityajati yadā yasmin kāle sarvān samastān kāmān icchā-bhedān he pārtha, mano-gatān manasi praviṣṭan hṛdi praviṣṭān |
and is satisfied with the True Inner most Self (Pratyag-ātman) in himself, without longing for external possessions, averse to everything else because of his acquisition of the immortal nectar, – i.e,, his realisation of the Supreme Truth, – then he is said to be a wise man (vidvan), one whose knowledge arising from the discrimination of the Self and the not-Self has been steadied. [If, on his abandoning of all desires, nothing should be found to cause satisfaction while the cause of the embodied state still operates, it would follow that his behaviour would be like that of a mad man or a maniac. Hence the words ‚ satisfied in the Self &c.]		sarva-kāma-parityāge tuṣṭi-kāraṇābhāvāt śarīra-dhāraṇa-nimitta-śeṣe ca sati unmatta-pramattasyeva pravṛttiḥ prāptā, ity ata ucyate – ātmany eva pratyag-ātma-svarūpe eva ātmanā svenaiva bāhya-lābha-nirapekṣas tuṣṭaḥ paramārtha-darśanāmṛta-rasa-lābhena anyasmād alaṃ-pratyayavān sthita-prajñaḥ sthitā pratiṣṭhitā ātmānātma-vivekajā prajñā yasya saḥ sthita-prajñaḥ vidvān tadā ucyate |
That is to say, he who has abandoned all desires connected with progeny, possessions and the world, who has renounced (all works), who delights in the Self and plays with the Self, – he is the man whose knowledge is steady.		tyakta-putra-vitta-lokaiṣaṇaḥ saṃnyāsī ātmārāma ātma-krīḍāḥ sthita-prajña ity arthaḥ ||2.55||

Rāmānuja

vṛtti-viśeṣa-kathanena svarūpam apy uktaṃ bhavati iti vṛtti-viśeṣocyate prajahātīti | ātmany evātmanā manasā ātmaikāvalambanena tuṣṭas tena toṣeṇa tad-vyatiriktān sarvān mano-gatān kāmān yadā prakarṣeṇa jahāti, tadāyaṃ sthita-prajña ity ucyate | jñāna-niṣṭhā-kāṣṭheyam

Śrīdhara

atra ca yāni sādhakasya jñāna-sādhanāni tāny eva svābhāvikāni siddhasya lakṣaṇāni | ataḥ siddhasya lakṣaṇāni kathayann evāntaraṅgāni jñāna-sādhanāny āha yāvad adhyāya-samāpti | tatra prathama-praśnasyottaram āha prajahātīti dvābhyām | manasi sthitān kāmān yadā prakarṣeṇa jahāti | tyāge hetum āha ātmanīti | ātmany eva svasminn eva paramānanda-rūpe ātmanā svayam eva tuṣṭa ity ātmārāmaḥ san yadā kṣudra-viṣayābhilāṣāṃs tyajati tadā tena lakṣaṇena muniḥ sthita-prajña ucyate

Madhusūdana

eteṣāṃ catūrṇāṃ praśnānāṃ krameṇottaraṃ bhagavān uvāca prajahātīti yāvad-adhyāya-samāpti | kāmān kāma-saṅkalpādīn mano-vṛtti-viśeṣān pramāṇa-viparyaya-vikalpa-nidrā-smṛti-bhedena tantrāntare pañcadhā prapañcitān sarvān niravaśeṣān prakarṣeṇa kāraṇa-bādhena yadā jahāti parityajati sarva-vṛtti-śūnya eva yadā bhavati sthita-prajñas tadocyate samādhistha iti śeṣaḥ | kāmānām anātma-dharmatvena parityāga-yogyatām āha manogatān iti | yadi hy ātma-dharmāḥ syus tadā na tyaktuṃ śakyeran vahny-auṣṇyavat svābhāvikatvāt | manasas tu dharmā ete | atas tat-parityāgena parityaktuaṃ śakyā evety arthaḥ |
nanu sthita-prajñasya mukha-prasāda-liṅga-gamyaḥ santoṣa-viśeṣaḥ pratīyate sa kathaṃ sarva-kāma-parityāge syād ity āha – ātmany eva paramānanda-rūpe na tv anātmani tuccha ātmnaā svaprakāśa-cid-rūpeṇa bhāsamānena na tu vṛttyā tuṣṭaḥ paritṛptaḥ parama-puruṣārtha-lābhāt | tathā ca śrutiḥ –
yadā sarve pramucyante kāmā ye ‚sya hṛdi śritāḥ |
atha martyo ‚mṛto bhavaty atra brahma samaśnute || [KaṭhU 2.3.14] iti |
tathā ca samādhi-sthaḥ sthita-prajña evaṃvidhair lakṣaṇa-vācibhiḥ śabdair bhāṣyata iti prathama-praśnasyottaram ||55||

Viśvanātha

atūrṇāṃ praśnānāṃ krameṇottaram āha prajahātīti yāvad adhyāya-samāptiḥ | sarvān iti kasminn apy arthe yasya kiṃcin mātro ‚pi nābhilāṣa ity arthaḥ | mano-gatān iti kāmānām ātma-dharmatvena parityāge yogyatā darśitā | yadi te hy ātma-dharmāḥ syus tadā tāṃs tyaktum aśakyeran vahner auṣṇyavad iti bhāvaḥ | tatra hetuḥ – ātmani pratyāhṛte manasi prāpto ya ātmānanda-rūpas tena tuṣṭaḥ | tathā ca śrutiḥ –
yadā sarve pramucyante kāmā ye ‚sya hṛdi śritāḥ |
atha martyo ‚mṛto bhavaty atra brahma samaśnute || [KaṭhU 2.3.14] iti

Baladeva

evaṃ pṛṣṭo bhagavān krameṇa catūrṇāṃ uttaram āha yāvad adhyāya-pūrtiḥ | tatra prathamasyāha prajahātīty ekena | he pārtha ! yadā mano-gatān manasi sthitān kāmān sarvān prajahāti saṃtyajati tadā sthita-prajña ucyate | kāmānām mano-dharmatvāt parityāgo yuktaḥ | ātma-dharmatve duḥśakyaḥ sa syād vahny-uṣṇatādīnām iveti bhāvaḥ |
nanu śuṣka-kāṣṭhavat kathaṃ tiṣṭhatīti cet tatrāha ātmany eveti | ātmani pratyāhṛte manasi bhāsamānena sva-prakāśānanda-rūpeṇātmanā svarūpeṇa tuṣṭaḥ paritṛptaḥ kṣudra-viṣayābhilāṣān saṃtyajyātmānandārāmaḥ samādhisthaḥ sthita-prajña ity arthaḥ |
ātmā puṃsi svabhāve ‚pi prayanta-manasor api |
dhṛtāv api manīṣāyāṃ śarīra-brahmaṇor api || iti medinī-kāraḥ |
brahma cātra jīveśvarānyatarad-grāhyam |