On this day, approx. 5000 years ago, on the battlefield of Kuruksetra, the Supreme Lord delivered the most confidential and topmost knowledge of devotional service to His lotus feet in the form of the Bhagavad-Gita to His dear most devotee Arjuna, and to humanity at large, in order to help all devotees understand the purpose of life and the way to surrender to Him. This day is also called Mokshada Ekadashi. It generally come in the month of December.