Matsya Purana — Vrata-Ṣaṣṭhī: The Sixty Sacred Vows
शिवरूपस्ततो ऽस्माभिः शिवलोके स मोदते एतद्देवव्रतं नाम महापातकनाशनम् //
śivarūpastato 'smābhiḥ śivaloke sa modate etaddevavrataṃ nāma mahāpātakanāśanam //
Thereafter, having assumed the form of Śiva through this observance, he rejoices in Śiva’s world. This is called the Devavrata, the vow that destroys even the greatest sins.
This verse does not address pralaya; it focuses on the fruit (phala) of a vow—attaining Śivaloka and the destruction of great sins.
It frames vrata as a dharmic discipline and a form of atonement (prayāścitta): a king or householder who has incurred grave faults is taught a sanctioned observance that purifies and restores religious merit.
The ritual significance is the Devavrata itself: it is presented as a powerful observance whose stated result is purification from mahāpātakas and the attainment of Śiva’s realm; no Vāstu or temple-building rule is mentioned in this specific verse.