Gita Jayanti is the day on which Lord Krishna spoke the Bhagavad-gita to Arjuna.
The Gita is also known as the Gitopanisad and is considered one of the Upanisads. The title Bhagavad-gita is sometimes translated as “The Song of God.” Gita means “song.” God, Krishna, is so sublime that whatever He speaks is music and poetry. The word bhagavan has been analyzed by Vedic authorities. Bhaga means “opulence” and is related to the word bhagya: “good fortune.” And van means “one who possesses.” So bhagavan means “He who possesses all opulence in full.”
viryasya yasasah sriyah
sannam bhaga itingana
“Full wealth, strength, fame, beauty, knowledge, and renunciation—these are the six opulences of the Supreme Personality of Godhead.” (Vishnu Purana 6.5.47)
All of us possess some wealth. I may have ten dollars, but if I look further, I will find someone who has a hundred dollars. And if I look still further, I will find someone who has a thousand dollars, and a million, and a billion. But no one can say that he has all the wealth in all creation, that no one is equal to him or greater than him in wealth. When we come to that person who has all wealth—no one is equal to or greater than him—that is Bhagavan, Krishna.
The Bhagavad-gita was originally spoken by Krishna to Arjuna. As stated in the Gita (4.1),
imam vivasvate yogam
proktavan aham avyayam
vivasvan manave praha
manur iksvakave ’bravit
“The Personality of Godhead, Sri Krishna, said: I instructed this imperishable science of yoga to the sun-god, Vivasvan, and Vivasvan instructed it to Manu, the father of mankind, and Manu in turn instructed it to Iksvaku.” Lord Krishna originally spoke the Gita to Vivasvan, the sun-god, who spoke it to his son Manu, who in turn spoke it to Iksvaku. In this way the knowledge was passed on through disciplic succession from one to the next to the next. But in the course of time, that chain became broken.
imam rajarsayo viduh
sa kaleneha mahata
yogo nastah parantapa
“This supreme science was thus received through the chain of disciplic succession, and the saintly kings understood it in that way. But in course of time the succession was broken, and therefore the science as it is appears to be lost.” (Gita 4.2) Nasta means “spoiled.” You may have a nice plate of prasada, but if you leave it aside and it becomes old and contaminated, it becomes nasta, spoiled. It is food, but you don’t get the benefit. And to get the real benefit of the Bhagavad-gita, one must receive it through parampara (evam parampara-praptam imam rajarsayo viduh).