BhG 4.21

syntax

[saḥ] (he) nirāśīḥ (free from desires) yata-cittātmā (whose mind and self are controlled) tyakta-sarva-parigrahaḥ (by whom all property is abandoned)
kevalam (merely) śārīram (bodily) karma (activities) kurvan (doing)
kilbiṣam (sin) na āpnoti (he does not obtain).

grammar

nir-āśīḥ	–	nir-ā-śis 1n.1 m. – who has no desires (from: niḥ – out of, away from, without; ā-√śās – to desire, āśis – desire, blessing);
yata-cittātmā	–	yata-citta-ātman 1n.1 m.; BV: yasya cittam ātmā ca yatau staḥ saḥ – whose mind and self are controlled (from: √yam – to hold back, to restrain, PP yata – held back, restrained; √cit – to perceive, to think, PP citta – thought; a thought, mind, heart, consciousness; ātman – self);
tyakta-sarva-parigrahaḥ	–	tyakta-sarva-parigraha 1n.1 m.; BV: yena sarve parigrahāḥ tyktāḥ santi saḥ – by whom all property is abandoned (from: √tyaj – to abandon, to give up, PP tyakta – abandoned; sarva – all, whole; pari-√grah – to take hold, to embrace, parigraha – taking, attaining, household, property);
śārīram	–	śārīra 2n.1 n. – bodily, related to body (from: √śri – to lean on, to rest on; or from: √śṝ – to break, to crush, śarīra – easy to be destroyed, the body);
kevalam	–	av. – only, merely (from: kevala – alone, simple, entire);
karma	–	karman 2n.1 n. – activity (from: √kṛ – to do);
kurvan	–	kurvant (√kṛ – to do) PPr 1n.1 m. – [while] doing;
na	–	av. – not;
āpnoti	–	√āp (to obtain) Praes. P 1v.1 – he obtains, he achieves;
kilbiṣam	–	kilbiṣa 2n.1 n. – fault, offence, sin;

textual variants

nirāśīr → yadāśīr (when desiring);
śārīraṁ → śarīraṁ (body);

The fourth pada of verse 4.21 is the same as the first pada of verse BhG 18.47;

Śāṃkara

yaḥ punaḥ pūrvokta-viparītaḥ prāg eva karmāmbhād brahmaṇi sarvāntare pratyag-ātmani niṣkriye saṃjātātma-darśanaḥ, sa dṛṣṭādṛṣṭeṣṭa-viṣayāśīr vivarjitatayā dṛṣṭādṛṣṭārthe karmaṇi prayojanam apyaśyan sa-sādhanaṃ karma saṃnyasya śarīra-yātrā-mātra-ceṣṭo yatir jñāna-niṣṭho mucyata iti | etad arthaṃ darśayitum āha—

nirāśīr nirgatā āśiṣo yasmāt sa nirāśīḥ | yata-cittātmā cittam antaḥ-karaṇam | ātmā bāhyaḥ kārya-karaṇa-saṃghātaḥ | tāv ubhāv api yatau saṃyatau yasya sa yata-cittātmā | tyakta-sarva-parigrahaḥ—tyaktaḥ sarvaḥ parigraho yena sa tyakta-sarva-parigrahaḥ | śārīraṃ śarīra-sthiti-mātra-prayojanaṃ kevalaṃ tatrāpi abhimāna-varjitaṃ karma kurvan | nāpnoti na prāpnoti kilbiṣam aniṣṭa-rūpaṃ pāpaṃ dharmaṃ ca | dharmo’pi mumukṣor aniṣṭa-rūpaṃ kilbiṣam eva | bandhāpādakatvāt | tasmāt tābhyāṃ mukto bhavati, saṃsārān mukto bhavatīty arthaḥ |

kiṃ ca śārīraṃ kevalaṃ karmety atra kiṃ śarīra-nirvartyaṃ śārīraṃ karmābhipretaṃ ? āho svic charīra-sthiti-mātra-prayojanaṃ śārīraṃ karma ? iti | kiṃ cāto yadi śarīra-nirvartyaṃ śārīraṃ karma yadi vā śarīra-sthiti-mātra-prayojanaṃ śarīraṃ ? iti | ucyate —yadā śarīra-nirvartyaṃ karma śārīram abhipretaṃ syāt tadā dṛṣṭādṛṣṭa-prayojanaṃ karma pratiṣiddham api śarīreṇa kurvan nāpnoti kilbiṣam iti bruvato viruddhābhidhānaṃ prasajyeta | śāstrīyaṃ ca karma dṛṣṭādṛṣṭa-prayojanaṃ śarīreṇa kurvan nāpnoti kilbiṣam ity api bruvato’prāpta-pratiṣedha-prasaṅgaḥ | śārīraṃ karma kurvan iti viśeṣaṇāt kevala-śabda-prayogāc ca vāṅ-manasa-nirvartyaṃ karma vidhi-pratiṣedha-viṣayaṃ dharmādharma-śabda-vācyaṃ kurvan prāpnoti kilbiṣam ity uktaṃ syāt |

tatrāpi vāṅ-manasābhyāṃ vihitānuṣṭhāna-pakṣe kilbiṣa-prāpti-vacanaṃ viruddham āpadyeta | pratiṣiddha-sevi-pakṣe’pi bhūtārthānuvāda-mātram anarthakaṃ syāt | yadā tu śarīra-sthiti-mātra-prayojanaṃ śārīraṃ karmābhipretaṃ bhavet, tadā dṛṣṭādṛṣṭa-prayojanaṃ karma vidhi-pratiṣedha-gamyaṃ śarīra-vāṅ-manasa-nirvartyam anyad akruvaṃs tair eva śarīrādibhiḥ śarīra-sthiti-mātra-prayojanaṃ kevala-śabda-prayogāt ahaṃ karomi ity abhimāna-varjitaḥ śarīrādi-ceṣṭā-mātraṃ loka-dṛṣṭyā kurvan nāpnoti kilbiṣam | evambhūtasya pāpa-śabda-vācya-kilbiṣa-prāpty-asambhavāt kilbiṣaṃ saṃsāraṃ nāpnoti | jñānāgni-dagdha-sarva-karmatvād apratibandhena mucyate eveti pūrvokta-samyag-darśana-phalānuvāda evaiṣaḥ | evaṃ śarīraṃ kevalaṃ karma ity asyārthasya parigrahe niravadyaṃ bhavati

Rāmānuja

punar api karmaṇo jñānākārataiva viśodhyate

nirāśīḥ nirgataphalābhisandhiḥ yatacittātmā yatacittamanāḥ tyaktasarvaparigrahaḥ ātmaikaprayojanatayā prakṛtiprākṛtavastuni mamatārahitaḥ, yāvajjīvaṃ kevalaṃ śārīram eva karma kurvan kilbiṣaṃ saṃsāraṃ nāpnoti jñānaniṣṭhāvyavadhānarahitakevalakarmayogenaivaṃrūpeṇātmānaṃ paśyatītyarthaḥ

Śrīdhara

kiṃ ca nirāśīr iti | nirgatā āśiṣaḥ kāmanā yasmāt | yataṃ niyataṃ cittam ātmā śarīraṃ ca yasya | tyaktāḥ sarve parigraho yena | sa śarīraṃ śarīra-mātra-nirvartyaṃ kartṛtvābhiniveśa-rahitaṃ kurvann api kilbiṣam bandhanaṃ na prāpnoti | yogārūḍha-pakṣe śārīra-nirvāha-mātropayogi svābhāvikaṃ bhikṣāṭanādi kurvann api kilbiṣaṃ vihitākaraṇa-nimitta-doṣaṃ na prāpnoti

Madhusūdana

yadātyanta-vikṣepa-hetor api jyotiṣṭomādeḥ samyag-jñāna-vaśān na tat-phala-janakatvaṃ tadā śarīra-sthiti-mātra-hetor avikṣepakasya bhikṣāṭanāder nāsty eva bandha-hetutvam iti kaimutya-nyāyenāha nirāśīr iti | nirāśīr gata-tṛṣṇo yata-cittātmā cittam antaḥkaraṇam ātmā bāhyendriya-sahito dehas tau saṃyatau pratyāhāreṇa nigṛhītau yena saḥ | yato jitendriyo ‚to vigata-tṛṣṇatvāt tyakta-sarva-parigrahas tyaktāḥ sarve parigrahā bhogopakaraṇāni yena saḥ | etādṛśo ‚pi prārabdha-karma-vaśāc chārīraṃ śarīra-sthiti-mātra-prayojanaṃ kaupīnācchādanādi-grahaṇa-bhikṣāṭanādi-rūpaṃ yatiṃ prati śāstrābhyanujñātaṃ karma kāyikaṃ vācikaṃ mānasaṃ ca, tad api kevalaṃ kartṛtvābhimāna-śūnyaṃ parādhyāropita-kartṛtvena kurvan paramārthato ‚kartrātma-darśanān nāpnoti na prāpnoti kilbiṣaṃ dharmādharma-phala-bhūtam aniṣṭaṃ saṃsāraṃ pāpavat puṇyasyāpy aniṣṭa-phalatvena kilbiṣatvam |

ye tu śarīra-nirvartyaṃ śārīram iti vyācakṣate tan mate kevalaṃ karma kurvann ity ato ‚dhikārthālābhād avyāvartakatvena śārīra-padasya vaiyarthyam | atha vācika-mānasika-vyāvartanātham iti brūyāt tadā karma-padasya vihita-mātra-paratvena śārīraṃ vihitaṃ karma kurvan nāpnoti kilbiṣam ity aprasakta-pratiṣedho ‚narthakaḥ | pratiṣiddha-sādhāraṇa-paratve ‚py evam eva vyāghāta iti bhāṣya eva vistaraḥ

Viśvanātha

ātmā sthūla-dehaḥ | śārīraṃ śārīra-nirvāhārthaṃ karmāsat-pratigrahādikaṃ kurvann api kilbiṣaṃ pāpaṃ nāpnotīty etad api vikarmaṇaś ca boddhavyam ity asya vivaraṇam

Baladeva

athārūḍhasya daśām āha nirāśīr iti tribhiḥ | nirgatā āśīḥ phalecchā yasmāt sa | yata-cittātmā vaśīkṛta-citta-dehas tyakta-sarva-parigraha ātmaikāvalokanārthatvāt prākṛteṣu vastuṣu mamatva-varjitaḥ | śārīraṃ karma śarīra-nirvāhārthaṃ karmāsat-parigrahādi kurvann api kilbiṣaṃ pāpaṃ nāpnoti