In plain words
The means of offering is Brahman, the oblation is Brahman, offered by Brahman into the fire of Brahman. Brahman alone is reached by one whose samādhi is Brahman-action.
Word for word
Brahman [is] the [means of] offering, brahman the oblation, offered by brahman in the fire of brahman; brahman alone is to be reached by him whose samādhi is in brahman-action.
The commentators
Bhagavadgītābhāṣyam
कस्मात् पुनः कारणात् क्रियमाणं कर्म स्वकार्यारम्भम् अकुर्वत् समग्रं प्रविलीयते इत्युच्यते यतः —
ब्रह्म अर्पणं येन करणेन ब्रह्मवित् हविः अग्नौ अर्पयति तत् ब्रह्मैव इति पश्यति, तस्य आत्मव्यतिरेकेण अभावं पश्यति, यथा शुक्तिकायां रजताभावं पश्यति ; तदुच्यते ब्रह्मैव अर्पणमिति, यथा यद्रजतं तत् शुक्तिकैवेति । ‘ब्रह्म अर्पणम्’ इति असमस्ते पदे । यत् अर्पणबुद्ध्या गृह्यते लोके तत् अस्य ब्रह्मविदः ब्रह्मैव इत्यर्थः । ब्रह्म हविः तथा यत् हविर्बुद्ध्या गृह्यमाणं तत् ब्रह्मैव अस्य । तथा ‘ब्रह्माग्नौ’ इति समस्तं पदम् । अग्निरपि ब्रह्मैव यत्र हूयते ब्रह्मणा कर्त्रा, ब्रह्मैव कर्तेत्यर्थः । यत् तेन हुतं हवनक्रिया तत् ब्रह्मैव । यत् तेन गन्तव्यं फलं तदपि ब्रह्मैव ब्रह्मकर्मसमाधिना ब्रह्मैव कर्म ब्रह्मकर्म तस्मिन् समाधिः यस्य सः ब्रह्मकर्मसमाधिः तेन ब्रह्मकर्मसमाधिना ब्रह्मैव गन्तव्यम् ॥
एवं लोकसङ्ग्रहं चिकीर्षुणापि क्रियमाणं कर्म परमार्थतः अकर्म, ब्रह्मबुद्ध्युपमृदितत्वात् । एवं सति निवृत्तकर्मणोऽपि सर्वकर्मसंन्यासिनः सम्यग्दर्शनस्तुत्यर्थं यज्ञत्वसम्पादनं ज्ञानस्य सुतरामुपपद्यते ; यत् अर्पणादि अधियज्ञे प्रसिद्धं तत् अस्य अध्यात्मं ब्रह्मैव परमार्थदर्शिन इति । अन्यथा सर्वस्य ब्रह्मत्वे अर्पणादीनामेव विशेषतो ब्रह्मत्वाभिधानम् अनर्थकं स्यात् । तस्मात् ब्रह्मैव इदं सर्वमिति अभिजानतः विदुषः कर्माभावः । कारकबुद्ध्यभावाच्च । न हि कारकबुद्धिरहितं यज्ञाख्यं कर्म दृष्टम् । सर्वमेव अग्निहोत्रादिकं कर्म शब्दसमर्पितदेवताविशेषसम्प्रदानादिकारकबुद्धिमत् कर्त्रभिमानफलाभिसन्धिमच्च दृष्टम् ; न उपमृदितक्रियाकारकफलभेदबुद्धिमत् कर्तृत्वाभिमानफलाभिसन्धिरहितं वा । इदं तु ब्रह्मबुद्ध्युपमृदितार्पणादिकारकक्रियाफलभेदबुद्धि कर्म । अतः अकर्मैव तत् । तथा च दर्शितम् ‘कर्मण्यकर्म यः पश्येत्’(भ. गी. ४ । १८) ‘कर्मण्यभिप्रवृत्तोऽपि नैव किञ्चित्करोति सः’(भ. गी. ४ । २०) ‘गुणा गुणेषु वर्तन्ते’(भ. गी. ३ । २८) ‘नैव किञ्चित्करोमीति युक्तो मन्येत तत्त्ववित्’(भ. गी. ५ । ८) इत्यादिभिः । तथा च दर्शयन् तत्र तत्र क्रियाकारकफलभेदबुद्ध्युपमर्दं करोति । दृष्टा च काम्याग्निहोत्रादौ कामोपमर्देन काम्याग्निहोत्रादिहानिः । तथा मतिपूर्वकामतिपूर्वकादीनां कर्मणां कार्यविशेषस्य आरम्भकत्वं दृष्टम् । तथा इहापि ब्रह्मबुद्ध्युपमृदितार्पणादिकारकक्रियाफलभेदबुद्धेः बाह्यचेष्टामात्रेण कर्मापि विदुषः अकर्म सम्पद्यते । अतः उक्तम् ‘समग्रं प्रविलीयते’(भ. गी. ४ । २०) इति ॥
अत्र केचिदाहुः — यत् ब्रह्म तत् अर्पणादीनि ; ब्रह्मैव किल अर्पणादिना पञ्चविधेन कारकात्मना व्यवस्थितं सत् तदेव कर्म करोति । तत्र न अर्पणादिबुद्धिः निवर्त्यते, किं तु अर्पणादिषु ब्रह्मबुद्धिः आधीयते ; यथा प्रतिमादौ विष्ण्वादिबुद्धिः, यथा वा नामादौ ब्रह्मबुद्धिरिति ॥
सत्यम् , एवमपि स्यात् यदि ज्ञानयज्ञस्तुत्यर्थं प्रकरणं न स्यात् । अत्र तु सम्यग्दर्शनं ज्ञानयज्ञशब्दितम् अनेकान् यज्ञशब्दितान् क्रियाविशेषान् उपन्यस्य ‘श्रेयान् द्रव्यमयाद्यज्ञात् ज्ञानयज्ञः’(भ. गी. ४ । ३३)‘श्रेयान् द्रव्यमयाद्यज्ञात् ज्ञानयज्ञः’(भ. गी. ४ । ३३) इति ज्ञानं स्तौति । अत्र च समर्थमिदं वचनम् ‘ब्रह्मार्पणम्’ इत्यादि ज्ञानस्य यज्ञत्वसम्पादने ; अन्यथा सर्वस्य ब्रह्मत्वे अर्पणादीनामेव विशेषतो ब्रह्मत्वाभिधानमनर्थकं स्यात् । ये तु अर्पणादिषु प्रतिमायां विष्णुदृष्टिवत् ब्रह्मदृष्टिः क्षिप्यते नामादिष्विव चेति ब्रुवते न तेषां ब्रह्मविद्या उक्ता इह विवक्षिता स्यात् , अर्पणादिविषयत्वात् ज्ञानस्य । न च दृष्टिसम्पादनज्ञानेन मोक्षफलं प्राप्यते । ‘ब्रह्मैव तेन गन्तव्यम्’ इति चोच्यते । विरुद्धं च सम्यग्दर्शनम् अन्तरेण मोक्षफलं प्राप्यते इति । प्रकृतविरोधश्च ; सम्यग्दर्शनम् च प्रकृतम् ‘कर्मण्यकर्म यः पश्येत्’(भ. गी. ४ । १८) इत्यत्र, अन्ते च सम्यग्दर्शनम् , तस्यैव उपसंहारात् । ‘श्रेयान् द्रव्यमयाद्यज्ञात् ज्ञानयज्ञः’ , ‘ज्ञानं लब्ध्वा परां शान्तिम्’(भ. गी. ४ । ३९) इत्यादिना सम्यग्दर्शनस्तुतिमेव कुर्वन् उपक्षीणः अध्यायः । तत्र अकस्मात् अर्पणादौ ब्रह्मदृष्टिः अप्रकरणे प्रतिमायामिव विष्णुदृष्टिः उच्यते इति अनुपपन्नम् | तस्मात् यथाव्याख्यातार्थ एव अयं श्लोकः ॥ २४ ॥
In plain words
But why is it that an action being performed dissolves completely, without even beginning to produce its own result? The answer is given: because —
'Brahman is the offering': the very ladle by which the knower of Brahman pours the oblation into the fire — he sees that this ladle, too, is nothing but Brahman. Apart from Brahman he sees it has no existence at all, the way you see that the 'silver' you thought you saw in a shell was never anything but the shell itself. That is why it is said, 'Brahman alone is the offering' — just as what looked like silver turns out to be mother-of-pearl. 'Brahman is the offering' — two separate words: whatever the world understands by 'offering' is, for this knower of Brahman, Brahman itself. Likewise 'Brahman is the oblation': whatever is understood by 'oblation' is, for him, Brahman alone. And 'in the fire that is Brahman' — one compound word: the fire itself, into which Brahman as the agent pours the offering, is Brahman — meaning Brahman alone is the one who acts. What is offered by that agent, the very act of offering, is Brahman. What is to be reached by that agent, the fruit itself, is also Brahman. 'By absorption in the action that is Brahman': action itself, seen as Brahman, is called Brahman-action, and one absorbed in it is called 'one absorbed in Brahman-action.' For such a person, Brahman alone is what is reached.
So even the action of someone working for the good of the world is, in the deepest sense, no action at all — because the very idea of Brahman has dissolved it. Given that, calling knowledge itself a 'sacrifice', simply to praise right vision, becomes all the more fitting, even for someone who has renounced every action. Whatever the world knows as 'offering' and so on with reference to outward ritual is, for the seer of ultimate truth, with reference to the Self, nothing but Brahman. Otherwise, if everything were already Brahman, there would be no point in singling out offering and the rest as specially Brahman. So for the knower who recognizes 'all this is Brahman alone,' there simply is no action — because there's no notion left of any factors of action at all. An act called 'sacrifice' with no sense of agent, instrument, and the rest simply isn't found anywhere. Every ordinary rite like the Agnihotra is performed with a sense of these factors — a deity assigned by the sacred word to receive the offering, and so on — and with the pride of being the doer and an eye on the fruit. No one is ever seen performing it with that sense of action, factor, and fruit dissolved, free of the pride of doership and any eye on reward. But the action spoken of here has exactly that dissolved by the notion of Brahman. So it is nothing but non-action. And this is exactly what is shown in verses like 'let him see inaction within action' (4.18), 'though busy acting, he does nothing at all' (4.20), 'the guṇas simply move among the guṇas' (3.28), and 'the knower of truth should think, disciplined, I do nothing at all' (5.8), among others. In teaching this, again and again, he dissolves that very sense of distinct action, factor, and fruit. We see the same thing elsewhere: in a desire-driven rite like the Agnihotra, if the desire itself dissolves, the rite is lost with it; and whether an act was done with deliberate intent or without shapes what particular result it can produce. In just the same way, for the knower whose sense of offering, factor, action, and fruit as separate things has dissolved into the notion of Brahman, even the bare outward motion of acting becomes, for him, no action at all. That is why it was said: 'the whole of it dissolves' (4.20).
Some scholars here offer a different reading: 'What is Brahman — that is the offering and the rest.' On their view, Brahman alone has taken the form of the five factors of action — the offering and so on — and it is Brahman, in that form, who performs the act. Here the ordinary notion of 'offering' isn't removed at all; instead, the notion of Brahman is simply laid over it — the way people project the notion of Viṣṇu onto a temple image, or the notion of Brahman onto a sacred syllable.
That's true — this reading would work if the whole passage weren't building toward praising the sacrifice of knowledge. But that's exactly what it's doing: after naming many particular rites 'sacrifice', the text introduces right vision itself as the true 'knowledge-sacrifice' and praises it — 'better than any sacrifice made of material substance is the sacrifice of knowledge' (4.33). Given that, the statement 'Brahman is the offering' and so on makes perfect sense as establishing knowledge's status as a sacrifice; otherwise, if everything were already Brahman, singling out offering and the rest for special mention would serve no purpose. As for those who say the notion of Brahman is simply projected onto offering and the rest, the way people project Viṣṇu onto a temple image or Brahman onto a sacred syllable — on their reading, this passage could not really be teaching the knowledge of Brahman meant here, because their 'knowledge' only ever has offering and the rest as its object, and no one reaches liberation through a knowledge that merely produces a mental picture. Yet the text itself says, 'Brahman alone is what is to be reached by him' — so it would be self-contradictory to claim liberation without real right vision. It also breaks with the flow of the whole passage: right vision has been the subject all along, as in 'let him see inaction within action' (4.18), and it is still the subject at the end, since everything in this stretch builds toward it. 'Better than a material sacrifice is the sacrifice of knowledge,' 'having gained knowledge, he attains supreme peace' (4.39), and so on — the whole chapter winds down praising nothing but right vision. It would make no sense for the text to suddenly, out of nowhere, claim that Brahman is merely being projected onto the offering and the rest, the way Viṣṇu is projected onto an image — that reading simply doesn't hold up. So this verse means exactly what has already been explained.
Close to the Sanskrit
But from what cause does action that is being performed, not making the beginning of its own effect, dissolve entirely? Thus it is said — because —
'Brahman is the offering' — the instrument, the ladle, by which the knower of Brahman offers the oblation into the fire, he sees that that instrument is Brahman alone — of it, apart from Brahman, he sees the non-existence, just as one sees the non-existence of silver in a piece of mother-of-pearl [apart from the shell itself]. So it is said: 'Brahman alone is the offering' — just as what looked like silver is really just mother-of-pearl. 'Brahman [is] the offering' — these are two uncompounded words: what is understood in the world by the notion 'offering', that, for this knower of Brahman, is Brahman alone — this is the meaning. 'Brahman [is] the oblation' — likewise, what is grasped by the notion 'oblation', that too, for this knower, is Brahman alone. Likewise, 'in the fire that is Brahman' — this is one compounded word. The fire itself, too, into which the offering is poured by Brahman as the agent, is Brahman alone — 'Brahman alone is the agent' is the meaning. What is offered by that agent, the very act of offering — that too is Brahman alone. What is to be reached by that agent, the fruit itself — that too is Brahman alone. 'By absorption in the Brahman-action' — action that is Brahman is called Brahman-action; one whose absorption is in that is 'one absorbed in Brahman-action'; by such a one, Brahman alone is to be reached.
Thus, even the action performed by one wishing the world's welfare is, in the highest sense, non-action, because it has been dissolved by the notion of Brahman. This being so, even for one who has ceased from all action, the renouncer, calling knowledge a 'sacrifice' for the sake of praising right vision becomes all the more fitting; what is well known as 'offering' and the rest with reference to the outer sacrifice, that, for one who sees the highest truth, is with reference to the Self, Brahman alone — such is the sense. Otherwise, if everything were Brahman, stating the Brahman-nature of offering and the rest specifically would be pointless. Therefore, for the knower who recognizes 'all this is Brahman alone', there is the absence of action — and because of the absence of any notion of factors of action. For an action called 'sacrifice' devoid of the notion of agent-factors is nowhere observed. Every action such as the Agnihotra is observed carrying the notion of agent-factors — the deity assigned by the sacred word as recipient, and so on — and carrying the conceit of agency and the intention for a fruit; never is one observed with that distinction of action, factor, and fruit dissolved, devoid of the conceit of agency and the intention for fruit. But this action here has precisely that distinction dissolved by the notion of Brahman. Therefore it is non-action alone. And this has been shown by such verses as 'let him see inaction in action' (4.18), 'though engaged in action he does nothing at all' (4.20), 'the guṇas move among the guṇas' (3.28), 'the knower of truth, disciplined, should think: I do nothing at all' (5.8), and others. And in showing this, he dissolves, at every such point, the notion of distinction between action, factor, and fruit. And it is observed that in the desire-motivated Agnihotra and the like, the dissolving of the desire itself destroys that rite; likewise, the capacity of actions done with or without deliberate intent to initiate a particular result is observed [to depend on such intent]. So too here: for the knower whose sense of the distinction of offering, factor, action, and fruit has been dissolved by the notion of Brahman, even the action that is mere outward movement becomes non-action. That is why it was said, 'the whole of it dissolves' (4.20).
Here some say: 'What is Brahman, that is the offering and the rest' — Brahman alone, indeed, having stood forth in fivefold factor-form as the offering and the rest, performs that very action. On this view, the notion of 'offering' and the rest is not removed; rather, the notion of Brahman is superimposed upon the offering and the rest — just as one superimposes the notion of Viṣṇu and the like upon an image, or just as one superimposes the notion of Brahman upon the sacred name and the like.
That is true; this too would hold, if the topic here were not the praise of the knowledge-sacrifice. But here, having introduced right vision — called the knowledge-sacrifice — as many particular rites called 'sacrifice', [the text] praises knowledge, saying 'better than a material sacrifice is the sacrifice of knowledge' (4.33). And here this statement, 'Brahman is the offering' and so on, is apt for establishing knowledge's status as sacrifice; otherwise, if everything were Brahman, stating the Brahman-nature of offering and the rest specifically alone would be pointless. As for those who say that, onto offering and the rest, the vision of Brahman is projected as one projects the vision of Viṣṇu onto an image, or as onto the sacred syllable and the like — for them, the knowledge of Brahman meant here would not have been intended, since their knowledge has only offering and the rest as its object; and liberation is never attained by a knowledge that merely produces a projected vision. Yet it is also said, 'Brahman alone is to be reached by him' — so it is contradictory to say that the fruit of liberation is attained without right vision. And it conflicts with the subject at hand: right vision itself is the topic, as in 'let him see inaction in action' (4.18), and it is right vision again at the end, since everything culminates precisely in that. 'Better than a material sacrifice is the sacrifice of knowledge', 'having gained knowledge, [he attains] supreme peace' (4.39), and so on — the chapter tapers off doing nothing but praising right vision. In that context, it would be senseless to suddenly claim that, regarding offering and the rest, out of context, the vision of Brahman is projected the way the vision of Viṣṇu is projected onto an image — this is untenable. Therefore, this verse has exactly the meaning already explained.