तदेतद्ब्रह्म क्षत्रं विट्शूद्रः ।तदग्निनैव देवेषु ब्रह्माभवद्ब्राह्मणो मनुष्येषु, क्षत्रियेण क्षत्रियः, वैश्येन वैश्यः, शूद्रेण शूद्रः ।तस्मादग्नावेव देवेषु लोकमिच्छन्ते ब्राह्मणे मनुष्येषु ।एताभ्यां हि रूपाभ्यां ब्रह्माभवत् ।अथ यो ह वा अस्माल्लोकात्स्वं लोकमदृष्ट्वा प्रैति स एनमविदितो न भुनक्ति यथा वेदो वाननूक्तोऽन्यद्वा कर्माकृतम् ।यदि ह वा अप्यनेवंविन्महत्पुण्यं कर्म करोति तद्धास्यान्ततः क्षीयत एव ।आत्मानमेव लोकमुपासीत ।स य आत्मानमेव लोकमुपास्ते न हास्य कर्म क्षीयते ।अस्माद्ध्येवात्मनो यद्यत्कामयते तत्तत्सृजते ॥बृह. १,४.१५ ॥
In plain words
These, then, are the priestly power, the ruling power, the people and the serving class. Among the gods Brahman came to be as fire, among men as the brahmin; as the man of the ruling class it came to be the ruling class; as the man of the people, the people; as the serving man, the serving class. Therefore men seek their world among the gods in fire and among men in the brahmin, for in these two forms did Brahman come to be. Now whoever departs from this world without having seen his own world — that world, being unknown, does not serve him, as an unrecited Veda or a rite left undone. Even if a man who does not know this performs a great and meritorious deed, that deed of his is spent at the last. Let a man worship the Self alone as his world. He who worships the Self alone as his world — his work is not spent; for out of this very Self he creates whatever he desires.
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam
न्तरं प्राप्य, क्षत्रियेण- क्षत्रियोऽभवत् इन्द्रादिदेवताधिष्ठि- तः, वैश्येन वैश्यः, शूद्रेण शूद्रः । यस्मात्क्षत्रादिषु विकारा- पन्नम्, अग्नौ ब्राह्मण एव चाविकृतं स्रष्टृ ब्रह्म, तस्मादग्ना- वेव देवेषु देवानां मध्ये लोकं कर्मफलम्, इच्छन्ति, अभिसंबद्धं कर्म कृत्वेत्यर्थः ; तदर्थमेव हि तद्ब्रह्म कर्मा- धिकरणत्वेनाग्निरूपेण व्यवस्थितम्; तस्मात्तस्मिन्नग्नौ कर्म कृत्वा तत्फलं प्रार्थयन्त इत्येतत् उपपन्नम् । ब्राह्मणे मनुष्येषु — मनुष्याणां पुनर्मध्ये कर्मफलेच्छायां ना- ग्न्यादिनिमित्तक्रियापेक्षा, किं तर्हि जातिमात्रस्वरूपप्रति- लम्भेनैव पुरुषार्थसिद्धिः ; यत्र तु देवाधीना पुरुषार्थसिद्धिः, तत्रैवाग्न्यादिसंबद्धक्रियापेक्षा; स्मृतेश्च — 'जप्येनैव तु सं- सिध्येद्ब्राह्मणो नात्र संशयः । कुर्यादन्यन्न वा कुर्यान्मैत्रो ब्राह्मण उच्यते' इति । पारिव्राज्यदर्शनाच्च । तस्माद्ब्राह्मणत्व एव मनुष्येषु लोकं कर्मफलमिच्छन्ति । यस्मादेताभ्यां हि ब्राह्मणाग्निरूपाभ्यां कर्मकर्त्रधिकरणरूपाभ्यां यत्स्रष्टृ ब्रह्म साक्षादभवन् ॥
अत्र तु परमात्मलोकमग्नौ ब्राह्मणे चेच्छन्तीति केचित् । तदसत्, अविद्याधिकारे कर्माधिकारार्थं वर्णविभागस्य प्र- स्तुतत्वात्, परेण च विशेषणात् ; यदि ह्यत्र लोकशब्देन धीतः कर्माद्यवबोधकत्वेन न भुनक्ति, अन्यद्वा लौकिकं कृ- ष्यादि कर्म अकृतं स्वात्मना अनभिव्यञ्जितम् आत्मीयफ- लप्रदानेन न भुनक्ति, एवमात्मा स्वो लोकः स्वेनैव नित्या- त्मस्वरूपेणानभिव्यञ्जितः अविद्याप्रहाणेन न भुनक्त्येव । ननु किं स्वलोकदर्शननिमित्तपरिपालनेन? कर्मणः फलप्रा- प्तिध्रौव्यात् इष्टफलनिमित्तस्य च कर्मणो बाहुल्यात् तन्निमि- त्तं पालनमक्षयं भविष्यति-तन्न, कृतस्य क्षयवत्त्वादित्येतदा- ह-यत् इह वै संसारे अद्भुतवत् कश्चिन्महात्मापि अनेवं- वित् स्वं लोकं यथोक्तेन विधिना अविद्वान् महत् बहु अश्व- मेधादि पुण्यं कर्म इष्टफलमेव नैरन्तर्येण करोति-अनेनैवा- नन्त्यं मम भविष्यतीति, तत्कर्म ह अस्य अविद्यावतः अविद्याजनितकामहेतुत्वान्न स्वप्रदर्शनविभ्रमोद्भूतविभूतवन् अन्ततः अन्ते फलोपभोगस्य क्षीयत एव ; तत्कारणयोर्वि- द्याकामयोश्चलत्वात् कृतक्षयध्रौव्योपपत्तिः । तस्मान्न पुण्य- कर्मफलपालनानन्त्याशा अस्त्येव । अत आत्मानमेव स्वं लो- कम्-आत्मानमिति स्वं लोकमित्यस्मिन्नर्थे, स्वं लोकमिति प्रकृतत्वात् इह च स्वशब्दस्याप्रयोगात्-उपासीत । स य आत्मानमेव लोकमुपास्ते-तस्य किमित्युच्यते-न हास्य कर्म क्षीयते, कर्माभावादेव-इति नित्यानुवादः ; यथा अविदुषः
In plain words
Through differentiation, the kshatriya manifested as the warrior class governed by deities like Indra, the vaishya as the merchant, and the shudra as the laborer. While those lower classes underwent modification, the brahmin alone—equated with fire—remains the unblemished creator Brahman. Therefore, it is among the gods in the sacrificial fire that people seek the fruits of action, for Brahman itself is established there as the altar of sacrifice. Thus, performing rites in that fire and seeking its reward is entirely appropriate. Among humans, however, attaining the highest human goal does not depend on external fire-rituals; rather, spiritual fulfillment is realized simply through the status of birth itself. Where attainment depends upon the deities, external fire-rituals are indeed required—as supported by the smriti text: 'Without doubt, a brahmin attains perfection through japa alone; whether he performs other rites or not, he is a true friend to all'—and as confirmed by the path of renunciation. Therefore, it is specifically within brahminhood among humans that people seek the fruit of action, for through these two forms—the brahmin and the sacrificial fire—the creator Brahman directly manifested as the agent and the altar.
Some argue that the 'world of the Supreme Self' refers to the sacrificial fire or the Brahmana. But this is incorrect. The division of social classes is introduced solely to establish eligibility for ritual action within the realm of ignorance, and the text explicitly qualifies this world as 'supreme'. If the word 'world' here meant something that does not sustain us because it merely reveals ritual actions, or if unperformed worldly actions like agriculture failed to sustain us because they remain unmanifested and cannot yield their fruits, then the Self—which is our true world—would indeed fail to sustain us if it remained unmanifested through our failure to destroy ignorance. One might ask: 'Why not simply rely on the preservation of our world through ritual actions? Since the fruits of rituals are guaranteed and such actions are abundant, will not the preservation they bring be everlasting?' No, because whatever is produced by action is inherently perishable. As the text says: 'If anyone in this transmigratory world, even a great soul, without this knowledge, performs vast and meritorious rituals like the horse-sacrifice continuously, thinking "This will bring me eternity," that action of his, born of ignorance and driven by desire, eventually wears out when its fruits are exhausted. It is not like the self-luminous glory of the Self. Since both ritual action and desire are unstable, whatever they produce must inevitably perish. Therefore, there is no hope of finding eternal security in the fruits of meritorious deeds. One must meditate on the Self alone as one's true world. He who meditates on the Self as his world finds that his work is never exhausted—not because his rituals last forever, but because he has transcended the very need for ritual action. This is a statement of eternal truth, unlike the state of the ignorant.
Close to the Sanskrit
Having attained interior, the kshatriya became the kshatriya presided over by deities headed by Indra, the vaishya by the vaishya, the shudra by the shudra. Since in the kshatriya and others it is modified, whereas in fire the brahmin alone is unblemished creator Brahman, therefore in fire alone among the gods in the midst of the gods they desire the world, the fruit of action, having performed connected action, such is the meaning; for that very purpose that Brahman is situated as the locus of action in the form of fire; therefore having performed action in that fire, that they pray for its fruit—this is proper. Among human beings—again in the midst of humans, in the desire for the fruit of action there is no need for action caused by fire and other factors, what then? The accomplishment of the human goal is attained simply by the acquisition of the nature of birth alone; whereas where the accomplishment of the human goal is dependent on the gods, there alone is the need for action connected with fire and others; and from smriti—'A brahmin should attain perfection by repetition alone, without doubt; whether he does other things or not, he is called a friendly brahmin'—and because of the observation of renunciation. Therefore in brahminhood alone among humans they desire the world, the fruit of action. Since by these two, the brahmin and fire forms, acting as agent and locus of action, which creator Brahman directly became.
But here, some desire the world of the Supreme Self in the fire or in the Brahmana. That is incorrect, because the division of classes is introduced for the purpose of eligibility for action in the sphere of ignorance, and because of the qualification by 'supreme'. If indeed here by the word 'world' that which is grasped does not protect by being the revealer of action etc., or other worldly action like agriculture, unperformed, does not protect by its own nature being unmanifested by giving its own fruit, in this way the Self, one's own world, unmanifested by its own eternal Self-nature, does not protect indeed by the destruction of ignorance. But is it not by the preservation caused by the vision of one's own world? Since the attainment of the fruit of action is certain, and because action which is the cause of desired fruit is abundant, the preservation caused by that will be imperishable—that is not so, because what is made is perishable, thus he says: 'that which here indeed in transmigratory existence, like a wonder, even some great soul, not knowing thus, ignorant of his own world according to the stated rule, performs great, abundant, meritorious action like the Ashvamedha, with desired fruit indeed, continuously—thinking "by this indeed endlessness will be mine", that action of his, who is ignorant, because of having desire produced by ignorance as its cause, not like the glory arisen from the delusion of self-revelation, in the end, at the end of the enjoyment of the fruit, is indeed exhausted; because of the instability of its two causes, knowledge and desire, the correctness of the certainty of the destruction of what is made is established. Therefore, there is indeed no hope of endlessness of the preservation of the fruit of meritorious action. Therefore, one should worship the Self indeed as one's own world—"the Self" in this sense of "one's own world", because "one's own world" is the topic, and here because of the non-use of the word "sva"—one should worship. He who worships the Self indeed as the world—what is said for him?—"his action is not exhausted", because of the very absence of action—thus it is a constant restatement; as of the ignorant.'