Bhashya
य एतं मन्त्रराजं नारसिंहमानुष्टुभं नित्यमधीते सोऽग्नि-ष्टोमेनोक्थ्येन षोडशिना वाजपेयेनातिरात्रेणाप्तोर्यामेणात्यग्नि-ष्टोमेनान्यैश्च सर्वैः क्रतुभिर्यजत इति फलनिर्देशः ।द्विरभ्या-सोऽध्यायसमाप्तिं द्योतयति ।न च वाच्यम् 'अन्यामर्थ-क्यात्' इति न्यायेन कथं फलनिर्देश इति ।यतो मनोव्या-पारैकसाध्यत्वादेतद्विद्यानुष्ठानस्य तस्य च कर्मानुष्ठानादत्य-न्तदुःसंपादत्वादित्यधिकारभेदेन नान्यानर्थक्यमिति सर्वंनिर्मलम् ॥
In plain words
'Recite this king of mantras daily and you have performed the Agniṣṭoma, the Ukthya, the Ṣoḍaśin, the Vājapeya, the Atirātra, the Āptoryāma, the Atyagniṣṭoma — every great rite there is.' That is the fruit named here, and the doubled line marks the chapter's end as usual. And no, this is not an empty repetition — someone might object that a fruit already promised elsewhere shouldn't need saying twice. But it should: this teaching can be accomplished by the mind alone, while those sacrifices demand elaborate ritual action that is brutally hard to carry out. Different people are equipped for different things, so nothing here is redundant. It all holds together.
Close to the Sanskrit
'Whoever recites this king of mantras, the Nārasiṃha anuṣṭubh, daily sacrifices by the Agniṣṭoma, the Ukthya, the Ṣoḍaśin, the Vājapeya, the Atirātra, the Āptoryāma, the Atyagniṣṭoma, and by every other rite besides' — this is the specification of the fruit. The double repetition signals the completion of the chapter. Nor should it be objected: by the maxim of the pointlessness of a repeated statement, how can there be a specification of a fruit here [since these rites already carry their own fruits]? Because the practice of this vidyā is accomplishable by mental effort alone, whereas that — the actual performance of the rites — is extremely difficult to accomplish, requiring [elaborate] ritual action; therefore, by this difference in eligibility, there is no redundancy in the other statement. Everything here holds together without contradiction.