In this incarnation, the Lord Vishnu manifested as a tortoise. The sage out of respect presented a garland of flowers to Indra who carelessly ignored his humbleness. Indra’s elephant trampled the garland, hence the sage in rage cursed Indra to lose all his wealth into the ocean.
To recover the lost treasures, the gods (Devas) and demons (Asuras) together churned the cosmic ocean (Samudra Manthan). They used Mount Mandara as a churning rod and the serpent Vasuki as a rope. However, without a base, the mountain began to sink. Lord Vishnu then took the form of a giant tortoise (Kurma) and provided his back as a stable foundation for the mountain.
From the churning emerged many divine treasures including Lakshmi (goddess of wealth), the divine physician Dhanvantari carrying the pot of amrita (nectar of immortality), and many other precious beings and substances.
Kurma Jayanti celebrates this divine avatar. Devotees observe fasting and worship Lord Vishnu in His Kurma form, seeking His blessings for stability, strength, and divine support in times of difficulty.