Matsya Purana — Glory of Tīrtha-Śrāddha: Best Times
तत्रैषा पितृभिर्गीता गाथा भागमभीप्सुभिः //
tatraiṣā pitṛbhirgītā gāthā bhāgamabhīpsubhiḥ //
In that context, this ancestral gāthā was sung by the Pitṛs for those who seek their rightful share through due rites and offerings.
This verse does not address pralaya; it introduces an ancestral maxim (Pitṛ-gāthā) connected to ritual entitlement—how the Pitṛs receive their due share through offerings.
It points to the householder’s (and by extension a king’s) duty to uphold Pitṛ-yajña: performing śrāddha and related rites so the ancestors receive their prescribed portion, sustaining dharma and family continuity.
Architectural meaning is not indicated; the ritual significance is that the text is about to cite a Pitṛ-authoritative gāthā explaining the principle of ‘bhāga’—the share due to ancestors in śrāddha/offerings.