Bhagawad Geeta is a part of Mahabharata. When Ved Vyas decided to write the Mahabharata, he appealed to Lord Ganesha , " O Ganesha, you become the author of my Mahabharata and I will tell you the Mahabharata. You please write it.
"लेखको भारतस्यास्य भव त्वं गणनायक
मय्यैव प्रोच्यमानस्य मनसा कल्पितस्य च "
This is the first verse of Adiparva in Mahabharata. मय्यैव प्रोच्यमानस्य....means I am writing the knowledge that I have acquired in the higher state of my mind, in the form of Mahabharata. O Ganesha you please become a writer to write it. Lord Ganesha immediately got ready. But he put one condition. He said " Ved Vyas, I will write your Mahabharata but will not stop anywhere while writing. Ved Vyas understood that Lord Ganesh is trapping him in words. But Ved Vyas was also clever. He said to Ganesha , " It is fine Ganesha, don't stop while writing. But I pray that you will not write further without understanding the true content of each of my verses." Lord Ganesha again got immediately ready. Lord Ganesha!! God of wisdom! There is nothing that Lord Ganesha is unable to understand. Because Lord Ganesha himself is true giver of wisdom. Ganesha said ,"Yes". Both Lord Ganesha and Vyas agreed to each other's terms and thus the writing of Mahabharata began. Vyas started telling and Lord Ganesha started writing. The first verse was praise of Ganesha. Lord Ganesha easily understood it. Ved Vyas now started reciting the Original Gita.
The background is that Kauravas and Pandavas have come to face to face for battle on the battlefield of Kurukshetra. Blind Dhrutrashtra (i. e. father of Kauravas) and Sanjaya are sitting in Hastinapur. Sanjay was given divine vision by Lord Krishna to see the war on the battlefield. With that divine vision Sanjay was going to tell Dhrutrashtra the description of the war. Dhrutrashtra asks Sanjay,
"धर्मक्षेत्रे कुरुक्षेत्रे समवेता युयुत्सव:
मामका: पांडवाश्चैव किमकुर्वत संजय"
Meaning is "All my sons and sons of Pandu have come face to face on Kurukshetra and Dharmakshetra. Sanjaya , you tell me it's description."
The very first verse of first chapter of Gita was recited by Ved Vyas and on this very first verse, Lord Ganesh stopped. Ganesh did not understand the meaning of this verse. Lord Ganesha wonder why Vyas gave two names to the same battlefield ? Dharmakshetra and Kurukshetra? Why these two names for same place ? Lord Ganesha started thinking over it. He was confused. He had to think a lot. So what was really so difficult about these two names that Lord Ganesha, the true giver of wisdom, God of wisdom, didn't understand?
So, to understand the two names Dharmakshetra and Kurukshetra, it is necessary to first understand what the word Kshetra means. Gita itself tells,
"इथं शरीरं तु कौन्तेय क्षेत्रमित्यभिधियते , एतद्यो वेत्ति तं प्राहु: क्षेत्रज्ञ इति तद्विद: "
The meaning is that this human body , this physical frame is said to be Kshetra i.e. field. And one who runs this field, this Kshetra, is the owner of the field i.e. क्षेत्रज्ञ ! And what is the war in this field , in this Kshetra? One battlefield where the war of Mahabharata was going to take place was Kurukshetra and other battlefield is this body , human body. Both have a lot in common. Both have two names Dharmakshetra and Kurukshetra. Kshetra means body. So why these two names to same body ?
Karma i. e. deed has to be done through this body. कुरू means deed, Karma. Hence the name Kurukshetra. Dharma is also to be performed through the same body, through the same Kshetra. Which Dharma? Humanity! Humanity, the only Dharma! This means the area to do Karma and the area to perform Dharma is same , i.e. this human body. So this body itself is Dharmakshetra and Kurukshetra. In this physical realm the battle is between good and bad i.e. good mind and evil mind. Good mind means Pandavas and evil mind means Kauravas. This is the battle of Mahabharata. And in this war , offcourse the victory will be for the good , i.e. Pandavas. Even in the battle of Kurukshetra Pandavas won. Therefore the war of Mahabharata and the war of good and evil mind in this human body are one and same.
It took Lord Ganesha a long time to understand the meaning of Dharmakshetra and Kurukshetra, and then Vyasa recited the next verse. The entire Mahabharata was written haltingly in this manner.
This Ganesha story is the key to understand the Bhagwad Gita. That's why Ved Vyas has written this Ganesh story . Ved Vyas wants to tell that the Gita which was not understood so easily by Lord Ganesha, the God of wisdom himself, how can be this Gita understood so easily by human beings? It means that the original content of Gita is something different, very profound. Those who practice Yogsadhana can understand it and those who do not do Yogsadhana cannot understand it. And if the content is not understood then such people say that Gita is false , there is nothing in Gita , etc. But the fact is that the Gita is a great book written only for the welfare of the entire human society which transcends caste and religion.
This deep meaning of Ganesh story of Mahabharata is explained by Great Yogi of 20th century, Yogi Manohar . Everyone should read Gita Vyas Meaning written by Yogi Manohar.