Bhashya
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 कर्मकृत्वा तत्फलं प्रार्थयन्त इत्येतत् उपपन्नम् ।ब्राह्मणेमनुष्येषु — मनुष्याणां पुनर्मध्ये कर्मफलेच्छायां ना-ग्न्यादिनिमित्तक्रियापेक्षा, किं तर्हि जातिमात्रस्वरूपप्रति-लम्भेनैव पुरुषार्थसिद्धिः ; यत्र तु देवाधीना पुरुषार्थसिद्धिः,तत्रैवाग्न्यादिसंबद्धक्रियापेक्षा; स्मृतेश्च — 'जप्येनैव तु सं-सिध्येद्ब्राह्मणो नात्र संशयः ।कुर्यादन्यन्न वा कुर्यान्मैत्रोब्राह्मण उच्यते' इति ।पारिव्राज्यदर्शनाच्च ।तस्माद्ब्राह्मणत्वएव मनुष्येषु लोकं कर्मफलमिच्छन्ति ।यस्मादेताभ्यां हिब्राह्मणाग्निरूपाभ्यां कर्मकर्त्रधिकरणरूपाभ्यां यत्स्रष्टृ ब्रह्मसाक्षादभवन् ॥
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.
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.