Matsya Purana — Inquiry into Yayāti’s Story and the Kacha–Devayānī Episode
पञ्च वर्षशतान्येवं कचस्य चरतो भृशम् तत्तत्तीव्रं व्रतं बुद्ध्वा दानवास्तं ततः कचम् //
pañca varṣaśatānyevaṃ kacasya carato bhṛśam tattattīvraṃ vrataṃ buddhvā dānavāstaṃ tataḥ kacam //
Thus, for five hundred years Kaca continued his arduous course of discipline. Recognizing the intensity of that severe vow, the Dānavas then turned their attention toward Kaca.
This verse does not discuss Pralaya; it highlights long-duration tapas/vrata as a moral-spiritual force that even hostile beings (the Dānavas) take seriously.
It underscores dharma through steadfast discipline: a king or householder is taught perseverance in vows (vrata), self-control, and consistency over time—qualities that stabilize personal conduct and governance.
No Vāstu or temple-building rule appears here; the ritual takeaway is the emphasis on the power of a ‘tīvra-vrata’ (severe observance) maintained continuously for a long period.