ऋचो यजूषि सामानीत्यष्टावक्षराणि ।अष्टाक्षरं ह वा एकं गायत्र्यै पदम् ।एतदु हैवास्या एतत् ।स यावतीयं त्रयी विद्या तावद्ध जयति योऽस्या एतदेवं पदं वेद ॥५,१४.२ ॥
In plain words
The Ṛc verses, the Yajus formulas, the Sāman chants — these are eight syllables, and one foot of the Gāyatrī has eight syllables; and this is that foot of hers. He who knows this foot of hers wins as much as this threefold knowledge is.
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· bhāṣya
तथा ऋचः यजूंषि सामाानीति त्रयीविद्यानामाक्षराणि एतान्यपि अष्टावेव ; तथैव अष्टाक्षरं ह वै एकं गायत्र्यै पदं द्वितीयम्, एतत् उ ह एव अस्या एतत् ऋग्यजुःसामलक्षणम् अष्टाक्षरत्वसामान्यादेव । सः यावती इयं त्रयी विद्या त्रय्या विद्यया यावत्फलजातम् आप्यते, तावत् ह जयति, योऽस्या एतत् गायत्र्याः त्रैविद्यलक्षणं पदं वेद ॥
In plain words
In the same way, Ṛk, Yajus, and Sāman give the syllables of the whole threefold learning, and they too come to eight. So this is the second foot of the Gāyatrī, eight-syllabled just like the first, and entirely hers — because both feet share that one measure. And whatever the threefold Veda earns, all of it, belongs to the one who knows this second foot for what it is.
Close to the Sanskrit
Likewise, ṛcaḥ, yajūṃṣi, sāmāni — these too, the syllables of the threefold knowledge, are eight only. Just so, 'eight-syllabled indeed is the one foot of the Gāyatrī' — this is the second [foot]. This indeed is hers, this one marked by Ṛk, Yajus and Sāman, precisely because of the shared feature of being eight-syllabled. 'As much as this threefold knowledge is' — whatever aggregate of fruit is obtained by the threefold knowledge, that much he conquers who thus knows this foot of hers, the one marked by the triple learning.