BhG 3.12

syntax

yajña-bhāvitāḥ (who are maintained by the sacrifice) devāḥ (the gods) vaḥ (to you) iṣṭān (desired) bhogān (enjoyments) dāsyante (they will give).
taiḥ [devaiḥ] hi (indeed by these gods) dattān (given) [bhogān] (enjoyments)
ebhyaḥ [devebhyaḥ] (to those gods) apradāya (after not offering) yaḥ (he who) bhuṅkte (he enjoys),
saḥ (he) stenaḥ eva (indeed a thief) [asti] (he is).

grammar

iṣṭān	–	iṣṭa (from: √iṣ – to desire or √yaj – to consecrate, to sacrifice, to worship) PP 2n.3 m. – desired, worshipped;
bhogān	–	bhoga 2n.3 m. – enjoyment, luxuries, wealth (from: √bhuj – to eat, to enjoy);
hi	–	av. – because, just, indeed, surely;
vaḥ	–	yuṣmat sn. 4i.3x – for you (shortened form of: yuṣmabhyam);
devāḥ	–	deva 1n.3 m. – the gods, divinities (from: √div – to shine, to play);
dāsyante	–	√dā (to give) Fut. Ā 1v.3 – they will give;
yajña-bhāvitāḥ	–	yajña-bhāvita 1n.3 m.; yajñena bhavitā iti – who are maintained by the sacrifice (from: √yaj – to consecrate, to sacrifice, to worship, yajña – sacrifice, worship, name of Viṣṇu; √bhū – to be, Caus.x PP bhāvita – created, maintained);
taiḥ	–	tat sn. 3n.3 m. – by them;
dattān	–	datta (√dā – to give) PP 2n.3 m. – given;
apradāya	–	na pra-√dā (to give away, to offer) absol. – after not offering;
ebhyaḥ	–	idam sn. 4i.3x m. – to them;
yaḥ	–	yat sn. 1n.1 m. – he who;
bhuṅkte	–	√bhuj (to eat, to enjoy) Praes. Ā 1v.1 – he eats, he enjoys;
stenaḥ	–	stena 1n.1 m. – a thief;
eva	–	av. – certainly, just, merely;
saḥ	–	tat sn. 1n.1 m. – he;

textual variants

bhogān → kāmān (enjoyments);
apradāyaibhyo → apradāyebhyo (not to be given);

Śāṃkara

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

Moreover,		kiṃ ca –
Nourished by the sacrifice, the Gods shall indeed bestow on you the enjoyments ye desire.” Whoso enjoys – without offering to Them – Their gifts, he is verily a thief.		iṣṭān bhogān hi vo devā dāsyante yajña-bhāvitāḥ | tair dattān apradāyaibhyo yo bhuṅkte stena eva saḥ ||3.12||
Pleased with your sacrifices, the Gods shall bestow on you all enjoyments, including women, cattle, children, &c.		iṣṭān abhipretān bhogān hi vo yuṣmabhyaṃ devā dāsyante vitariṣyanti strī-paśu-putrādīn yajña-bhāvitā yajñair vardhitās toṣitā ity arthaḥ |
He who enjoys what is given by Gods, i.e., he who gratifies the cravings of his own body and senses without discharging the debt due to the Gods, is a thief indeed, a robber of the property of the Gods, &c.		tair devair dattān bhogān apradāyādattvā, ānṛṇyam akṛtvety arthaḥ ebhyo devebhyaḥ yo bhuṅkte sva-dehendriyāṇy eva tarpayati stena eva taskara eva sa devādi-svāpahārī ||3.12||

Rāmānuja

yajñabhāvitāḥ yajñenārādhitāḥ madātmakā devāḥ iṣṭān vo dāsyante uttamapuruṣārthalakṣaṇaṃ mokṣaṃ sādhayatāṃ ye iṣṭā bhogās tān pūrvapūrvayajñabhāvitā devā dāsyante uttarottarārādhanopekṣitān sarvān bhogān vo dāsyante ityarthaḥ / svārādhanārthatayā tair dattān bhogān tebhyo ‚pradāya yo bhuṅkte cora eva saḥ / couryaṃ hi nāma anyadīye tatprayojanāyaiva parikḷpte vastuni svakīyatābuddhiṃ kṛtvā tena svātmapoṣaṇam / ato ‚sya na paramapuruṣārthānarhatāmātram; api tu nirayagāmitvaṃ ca bhaviṣyatītyabhiprāyaḥ

Śrīdhara

etad eva spaṣṭīkurvan karmākaraṇe doṣam āha iṣṭān iti | yajñair bhāvitāḥ santo devā vṛṣṭy-ādi-dvāreṇa vo yuṣmabhyaṃ bhogān dāsyante hi | ato devair dattān annādīn ebhyo devebhyaḥ pañca-yajñādibhir adattvā yo bhuṅkte, sa stenaś caura eva jñeyaḥ

Madhusūdana

na kevalaṃ pāratrikam eva phalaṃ yajñāt, kintv aihikam apīty āha iṣṭān iti | abhilaṣitān bhogān paśv-anna-hiraṇyādīn vo yuṣmabhyaṃ devā dāsyante vitariṣyanti | hi yasmād yajñair bhāvitās toṣitās te | yasmāt tair ṛṇavad bhavadbhyo dattā bhogās tasmāt tair devair dattān bhogān ebhyo devebhyo ‚pradāya yajñeṣu devodeśenāhutīrasampādya yo bhuṅkte dehendriyāṇy eva tarpayati stena eva taskara eva sa deva-svāpahārī devārṇapākaraṇāt

Viśvanātha

etad eva spaṣṭīkurvan karmākaraṇe doṣam āha iṣṭān iti | tair dattān vṛṣṭy-ādi-dvāreṇānnādīn nādīn utpādety arthaḥ | ebhyo devebhyaḥ pañca-mahā-yajñādibhir adattvā yo bhuṅkte, sa tu caura eva

Baladeva

etad eva viśadayan karmānuṣṭhānena doṣam āha iṣṭān iti | pūrva-bhāvita-mad-aṅga-bhūtā devā vo yuṣmabhyam iṣṭān mumukṣu-kāmyān uttarottara-yajñāpekṣān bhogān dāsyanti vṛṣṭy-ādi-dvārā vrīhy-ādīn utpādyety arthaḥ | svārcanārthaṃ tair devair dattāṃs tān bhogān ebhyaḥ pañca-yajñādibhir apradāya kevalātma-tṛpti-karo yo bhuṅkte sa stenaś caura eva | devas tāny apahṛtya tair ātmanaḥ poṣāt | cauro bhūpād iva sa yamād daṇḍam arhati pumarthānarhaḥ