Matsya Purana — Manvantaras
यथान्धकारे खद्योतः सहसा सम्प्रदृश्यते तथा निवृत्तो ह्यव्यक्तः खद्योत इव संज्वलन् //
yathāndhakāre khadyotaḥ sahasā sampradṛśyate tathā nivṛtto hyavyaktaḥ khadyota iva saṃjvalan //
As a firefly is suddenly seen in the darkness, so too the Unmanifest (Avyakta)—when the mind turns back from outward objects—shines forth, blazing like a firefly.
It points to the Avyakta (unmanifest) as a subtle ground that is not grasped outwardly; it becomes evident when perception withdraws inward—an idea often used to explain how the causal state underlies manifestation and withdrawal.
It emphasizes nivṛtti (inner restraint and withdrawal from excessive sense-pursuit). For a king or householder, this supports disciplined governance and ethical living: act in the world, yet regularly return the mind inward through self-control and contemplation.
No direct Vāstu or ritual rule is stated; the imagery functions as a contemplative instruction—ritual and discipline are implied as supports for inward turning, by which subtle truth becomes perceptible.