Matsya Purana — Catalogue of the Eighteen Puranas
तथाष्टादशधा कृत्वा भूर्लोके ऽस्मिन्प्रकाश्यते अद्यापि देवलोके ऽस्मिञ् छतकोटिप्रविस्तरम् //
tathāṣṭādaśadhā kṛtvā bhūrloke 'sminprakāśyate adyāpi devaloke 'smiñ chatakoṭipravistaram //
Thus, having been divided into eighteen parts, it is made manifest here in Bhūrloka, the world of mortals; and even now, in Devaloka, the world of the gods, it remains expanded to a vast extent—of a hundred koṭis in measure.
It does not describe Pralaya directly; instead, it emphasizes the Purāṇa’s transmission across realms—being promulgated on earth while retaining a far greater, ‘expanded’ form in the divine realm.
Indirectly, it supports dharma by stressing that authoritative teachings are ‘made manifest’ for Bhūrloka—implying that rulers and householders should rely on the accessible, transmitted Purāṇic instruction for right conduct.
No specific Vāstu or ritual procedure is mentioned; the key point is textual—division into eighteen and the idea of an original, larger divine recension versus an earthly promulgated form.