याज्ञवल्क्येति होवाच कतिभिरयमद्य ब्रह्मा यज्ञं दक्षिणतो देवताभिर्गोपायतीति ।एकयेति ।कतमा सैकेति ।मन एवेति ।अनन्तं वै मनोऽनन्ता विश्वे देवाः ।अनन्तमेव स तेन लोकं जयति ॥बृह. ३,१.९ ॥
In plain words
"Yājñavalkya," he said, "by how many deities does the Brahman priest guard the sacrifice today on the south?" "By one." "Which is that one?" "The mind alone. For the mind is endless and the All-gods are endless; and by it he wins an endless world."
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· bhāṣya
याज्ञवल्क्येति होवाचेति पूर्ववत् । अयम् ऋत्विक् ब्रह्मा दक्षिणतो ब्रह्मा आसने स्थित्वा यज्ञं गोपायति । कति- भिर्देवताभिर्गोपायतीति प्रासङ्गिकमेतद्बहुवचनम्- एकया—
In plain words
'Yājñavalkya,' he said — the same opening as before. This priest, the Brahmā officiant seated on the south side, takes his seat and watches over the sacrifice. 'By how many deities does he guard it?' — that plural is simply a quirk of how the question is phrased; the real answer is 'By one—'
Close to the Sanskrit
'Yājñavalkya,' said [he] — as before. This officiant, the Brahmā priest, the Brahmā priest on the south side, having taken his seat, guards the sacrifice. 'By how many deities does he guard it?' — this plural [wording] is merely incidental to the context [of the question]; [the true answer is] 'By one—'