वागेव ब्रह्मणश्चतुर्थः पादः सोऽग्निना ज्योतिषा भाति च तपति च भाति च तपति च कीर्त्या यशसा ब्रह्मवर्चसेन य एवं वेद ॥ ३.१८.३ ॥
In plain words
Speech is one of the four feet of Brahman; it shines and burns with fire for its light. He who knows this shines and burns with renown, with glory and with the lustre of Brahman.
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
तत्र वागेव मनसो ब्रह्मणश्चतुर्थ पाद । माऽग्निना अ धिदैवतेन ज्योतिषा भाति च दीप्यते तपति च संताप च औष्ण्य करोति । अथवा तैलघृताद्याग्नेयाशनेन इद्धा वाग्भाति च तपति च वदनायोत्साहवती स्यादित्यर्थ । विद्वत्फलम्, भाति च तपति च कीर्त्या यशसा ब्रह्मवर्चसेन, य एव यथाक्त वेद ॥
In plain words
Here, speech is the fourth quarter of the mind-Brahman. Linked with cosmic fire and light, it radiates, blazes, and warms. Or alternatively, nourished by wholesome food, the faculty of speech becomes vibrant and eloquent. And the fruit for the wise seeker who knows this in the prescribed way is that he shines and radiates with fame, glory, and spiritual splendor.
Close to the Sanskrit
There, speech alone is the fourth quarter of the mind-Brahman. Associated with fire as the cosmic deity, with light, it shines and flames and heats and produces warmth and temperature. Or else, kindled by the consumption of oily and ghee-like fiery food, speech shines and heats and becomes vigorous for speaking—this is the meaning. The fruit for the knower: he shines and heats with fame, with glory, with spiritual luster, who thus knows as stated.