Vishnu's Sleep and the Season of Rain

Puranic literature frames the four months of Chaturmasya around a single governing image: Vishnu withdraws into yogic sleep upon the coiled serpent Shesha, floating in the cosmic ocean, from Devshayani Ekadashi, literally the Ekadashi on which the god lies down, until Devutthana or Prabodhini Ekadashi, the Ekadashi of his rising. During this interval the god is understood to have withdrawn active oversight of worldly affairs, and Hindu tradition has long treated the period as unsuitable for auspicious undertakings that would ordinarily seek divine sanction, weddings, house warmings and other major life cycle rites chief among them, which are conventionally deferred until Vishnu wakes.

The devotional explanation sits alongside a practical seasonal one that scholars of the Hindu calendar generally treat as at least as important to the observance's origin. The four months of Chaturmasya correspond closely to the monsoon across most of the subcontinent, a season in which travel on foot became difficult or dangerous, rivers rose, and roads and paths were washed out or overgrown, conditions that gave a wandering ascetic or itinerant teacher good practical reason to stop moving regardless of what the devotional calendar said about a sleeping god.