The "Bhagavad-Gita", if some don't know, is:
The title "Bhagavad-Gita" translates as, the "Song of God";
It's 700 Verses long;
It's a chapter in the Mahabharata [the epic history of the Royal Dynasty of ancient India circa 3,000 BCE];
This chapter occurs after years of court intrigue and repeated attempts of assasination of a family of 5 younger cousins by the older group of cousins.
The entire world finally took sides after decades of attempts at reconciliation ---and thus, civil-war was declared for the helm of the Royal Aryan Dynasty of the Ancient world 3,000 BCE.
On the first day of the battle ---the General on one side asked to veiw the two opposing sides ---and then suddenly this Prince, named Arjuna, fell silent and sat down.
Thus, Arjuna's cousin & then chariot driver, Lord Krishna, turned to Arjuna to seek to remedy the sudden lack of determination that had overcome Arjuna just as the war had already technically begun.
The 5 Topics addressed in the Gita are:
1 Jiva (nature of the Soul)
2 karma (nature of the Actions)
3 kala (nature of the time)
4 Prakriti (nature of the material Matter & Energy)
5 isvara (nature of the God [the Controller])
Krishna spoke to Arjuna, confidentially for approx 2 1/2 Hours ---while the readied warring parties stood aside and awaited the end of the postponment caused by Arjuna's sudden in-action.
After the "Gita" was finished being spoken by Krishna to Arjuna, the war proceeded for 18 days. What occurred for each of the 18 days and the events after the war was over are all recorded for posterity in the remainder of the Mahabharata.
The Gita is the Bible of Hinduism because it was a summary of Yoga Knowledge as it is; and it was directly spoken by God himself when he advented in his Original-Original Form as Krishna; and it is from the Royal History Epic of India's ancient past known as the "Maha-Bharata" ("Great-Bharata" ~named after the namesake of the famous past Empereor Maharaja (King) 'Bharata'; BTW, the actual name for India, in the country of India is "Bharata". You'll find that India's actual name, 'Bharata' is on all Indian Post Stamps).