Gita Jayanti is believed to be the birthday of the Bhagavad Gita, The Song of the God. Here is a short write up on the essence of Bhagavad Gita:
Perform your duty with no attachment to the result of your action, to the world, or its sense gratification. The purpose of life is to merge with your Source, the divine. One can achieve that through any of the following: the pursuit of knowledge (Jnana Yoga), or selfless action (without being attached to the fruits of your action – Karma Yoga), or Devotion (Bhakti Yoga).
Some of the beautiful verses from Gita:
A true Yogi observes Me in all beings and also sees every being in Me. Indeed, the self-realized person sees Me, the same Supreme Lord, everywhere – Gita 6:29
Whatever form [or formlessness] any devotee with faith, wishes to worship, I surely sustain firmly that faith in him. It does not matter whichever religions or faiths you follow, as long as you have faith in what you follow, you will attain Moksha / liberation / freedom from the endless cycle of births and deaths. – Gita 7:21
vasamsi jirnani yatha vihaya
navani grhnati naro ’parani
tatha sarirani vihaya jirnany
anyani samyati navani dehi
As a person puts on new garments, giving up old ones, the soul similarly accepts new material bodies, giving up the old and useless ones. – Gita 2:22
krodhād bhavati sammohaḥ
From anger, complete delusion arises, and from delusion bewilderment of memory. When memory is bewildered, intelligence is lost, and when intelligence is lost one falls down again into the material pool. – Gita 2:63
bandhur atmatmanas tasya
anatmanas tu satrutve
For someone who has conquered the mind, the mind becomes the best friend; but for one who has failed to do so, the very same mind will be his greatest enemy. – Gita 6:6
Happy Gita Jayanti.