In Yester era accomplished sages and Rishis deeply immersed in thoughts of God Almighty to reach cosmic truths of life contained within. To contemplate (indulge in chintan) on vital issues of life in isolation these sages and Rishis often went to deep dense forests in Himalayas.
It is then these sages and Rishis discovered that there was more to life than simply indulging in religious practices (rituals) all the time.
It is in such times these highly advanced sages and Rishis directly invoked messages from God, the first words of God Almighty to mankind we now know as Vedas (Hinduism revelations). All the four Vedas (Rig Veda, Sama Veda Yajur Veda and Atharva Veda) were invoked over a long period of time. But one problem existed; all the Vedas were voluminous even beyond comprehension of most learned scholars.
And thus started indulgence of sages and Rishis in individual precepts of spirituality contained in Vedas and various Upanishads (independent spiritual treatises) came into existence. Over 200 Upanishads existed in present times of which 11 are primary.
Commentaries on all these principle Upanishads including Bhagavad Gita is available from Gita press, Gorakhpur, India from none other than Adi Shankaracharya, an enlightened one. All the publications from Gita press are highly subsidized available at prices ranging from $1 to $6.
The earlier problem still existed. Learned scholars still failed to reach the underlying meaning of sacred texts contained in Upanishads. The jnana wisdom contained in Vedas and Upanishads just did not reach the masses. And finally God Almighty, Brahman obliged the entire mankind.
And advent Lord Krishna, an avatar of his era during Dwapar Yuga, a time of great strife, tribulation! And in the battle of Mahabharata at opportune moment outpoured sermon of Bhagavad Gita to Arjuna, the Pandava prince!
Finally the wisdom of ages reached masses, commoners and that too in totality. In present times particularly in India one can see the gist of Bhagavad Gita, the essence of Bhagavad Gita hung in all bookstores and in many houses.
With the advent of Lord Krishna, a savior messiah the circle of life finally completed. Human beings finally realized the value of spirituality compared to religion.