स य एवमेतद्यज्ञायज्ञीयमङ्गेषु प्रोतं वेदाङ्गी भवति नाङ्गेन विहूर्छति सर्वमायुरेति ज्योग्जीवति महान्प्रजया पशुभिर्भवति महान्कीर्त्या संवत्सरं मज्ज्ञो नाश्नीयात्तद्व्रतं मज्ज्ञो नाश्नीयादिति वा ॥ २.१९.२ ॥
In plain words
He who knows the Yajñāyajñīya chant thus woven upon the limbs comes to have sound limbs and is not maimed in any limb, reaches his full span of life, lives long, becomes great in offspring and cattle, great in renown. Let him not eat marrow for a year: that is the vow — or rather, let him not eat marrow at all.
The commentators
Chāndogyopaniṣadbhāṣyam· bhāṣya
अङ्गी भवति समग्राङ्गो भवतीत्यथ । नाङ्गेन हस्तपादा- दिना विहूर्च्छति न कुटिलीभवति, पङ्गु कुणी वा इत्यर्थ । संवत्सर संवत्सरमात्र मज्ज्ञो मांसानि नाश्नीयात् न भक्ष- येत् । बहुवचन मत्स्योपलक्षणार्थम् । मज्ज्ञो नाश्नीयात् सर्वदैव नाश्नीयादिति वा, तद्व्रतम् ॥
In plain words
He becomes complete in his limbs—fully formed, that is the sense. He suffers no failure in any limb, whether hand or foot; he is neither bent nor crippled nor lame. For a full year he avoids eating marrow and flesh, touching neither. The plural form implies fish as well. He must abstain from marrow, or rather, avoid it altogether; this is the vow.
Close to the Sanskrit
He becomes possessed of limbs, complete-limbed he becomes, thus is the meaning. He does not falter with any limb such as hand or foot, nor does he become crooked, lame or maimed, such is the meaning. For a year or year-measure he should not eat marrow and flesh, nor consume them. The plural is for the sake of indicating fish. Marrow he should not eat, or he should never eat it at all, that is the vow.