Bhashya
य एतं मन्त्रराजं नारसिंहमानुष्टुभं नित्यमधीते सभूर्भुवःस्वर्महर्जनस्तपःसत्यमन्यच्च सर्वं पाताललोकं जय-तीति फलनिर्देशः ।द्विरभ्यासोऽध्यायसमाप्तिं द्योतयति ॥
In plain words
All seven worlds — earth, the mid-region, heaven, the great realm, the realm of beings, austerity, truth — and, besides those, the netherworld too: daily recitation of this king of mantras wins every one of them. That is the fruit spelled out here. And the doubled line marks the chapter's end, as it always does.
Close to the Sanskrit
'Whoever recites this king of mantras, the Nārasiṃha anuṣṭubh, daily conquers the earth-realm, the mid-realm, the heaven-realm, the great realm, the realm of created beings, the realm of austerity, the realm of truth, and anything else — the netherworld realm as well, all of it' — this is the specification of the fruit. The double repetition signals the completion of the chapter.