On this full-moon day, sixteen days before Ratha- yatra, Lord Jagannatha is bathed. He becomes sick and is confined to rest for fourteen days. He is then offered special care until He comes out for Ratha-yatra.
A special bath of Jagannatha takes place on the Purnima of Jyestha month to commemorate the appearance day of Lord Jagannatha.
According to Skanda Purana, when King Indradyumna installed the wooden deities he arranged this bathing ceremony. This day is considered to be the birth-day of Lord Jagannatha.
It is said that a staunch devotee of Lord Ganesh and himself a profound scholar visited Puri during Snana Yatra. He was amply rewarded by the King of Orissa for his scholarship.
The King asked the scholar to accompany him to see Lord Jagannatha, which he refused under the pretext that he wouldn’t worship any “God” other than his Ishtha-devata, Ganesh.
Somehow he was persuaded and brought before the Snana vedi. To the utter surprise of all, Lord Jagannatha appeared with an elephantine form that resembled Ganesh.
Since then, during Snana Yatra when the sacred bath is performed, the Deities are dressed like elephants – resembling Ganesh.