कतमे षडिति ।अग्निश्च पृथिवी च वायुश्चान्तरिक्षश्चादित्यश्च द्यौश्चैते षट् ।एते हीदं सर्वं षडिति ॥बृह. ३,९.७ ॥
In plain words
"Which are the six?" "Fire and the earth, the wind and the middle region, the sun and the sky — these are the six, for all this is these six."
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· bhāṣya
कतमे षडिति । त एव अग्न्याद्या वसुत्वेन पठिताः चन्द्रमसं नक्षत्राणि च वर्जयित्वा षड्भवन्ति- षट्संख्या- विशिष्टाः । एते हि यस्मात्, त्रयस्त्रिंशदादि यदुक्तम् इदं सर्वम्, एत एव षड्भवन्ति; सर्वो हि वस्वादिविस्तर एतेष्वेव षट्सु अन्तर्भवतीत्यर्थः ॥
In plain words
‘And which are the six?’ The very same beings that were listed under the Vasus — only now, leaving out the Moon and the stars — come down to six. And why does that matter? Because everything said earlier, all the way from the thirty-three gods onward, ultimately folds into just these six. The whole sprawling account, starting from the Vasus, is finally contained within these six alone — that is the point being made.
Close to the Sanskrit
'Which are the six?' — Those very same [deities] enumerated as the Vasus, excluding the Moon and the constellations, become six — characterized by the number six. For since these, all that was said beginning with the thirty-three, [reduces to] these very ones becoming six; for the entire elaboration beginning with the Vasus is included within just these six — that is the meaning.