Matsya Purana — Catalogue of the Eighteen Puranas
उपभेदान्प्रवक्ष्यामि लोके ये सम्प्रतिष्ठिताः पाद्मे पुराणे यत्रोक्तं नरसिंहोपवर्णनम् तच्चाष्टादशसाहस्रं नारसिंहमिहोच्यते //
upabhedānpravakṣyāmi loke ye sampratiṣṭhitāḥ pādme purāṇe yatroktaṃ narasiṃhopavarṇanam taccāṣṭādaśasāhasraṃ nārasiṃhamihocyate //
I shall now declare the subsidiary divisions (upabhedas) that are well established in the world. That account in the Padma Purāṇa where the description of Narasiṁha is taught—consisting of eighteen thousand verses—is here called the Nārasiṁha (Purāṇa).
This verse does not discuss pralaya; it classifies Purāṇic literature by naming an upabheda (the Nārasiṁha text) and giving its extent (18,000 verses).
Indirectly, it supports dharma by identifying authoritative textual sources: knowing recognized Purāṇas/upapūrāṇas guides kings and householders in choosing reliable narratives and teachings for ritual, vows, and conduct.
No specific vastu or ritual procedure is stated; the significance is bibliographic—pointing to a recognized Narasiṁha-focused Purāṇic corpus used for devotion and related observances.