The Bhagavad Gita is one of the essential texts on bhakti yoga (devotion) for Vaisnava Hindus. It is in fact probably the most universally accepted of all Hindu scriptures regardless of the sect --
http://www.allfaith.com/Religions/Hinduism/gita.html
The story takes place on a battlefield. Arjuna is one of the world's most accomplished warriors, however due to the nature of this civil war he had relatives, friends and teachers on both side.
Sri Krsna, who is God Incarnate, had agreed to act as Arjuna's chariot driver. The reason why he did so is explained in the introduction to my translation
( http://www.allfaith.com/Religions/Hinduism/gitaintro.html).
Seated in the chariot and looking at the assembled armies, Arjuna says to Sri Krsna: I will not fight!
This is basically how the Gita begins. The "Song of God" is Sri Krsna's reply to this refusal.
Sri Krsna explains that there are many ways (yoga systems) to seek enlightenment. He lists several possibilities in some detail, but none of them satisfy Arjuna.
Sri Krsna then reveals to Arjuna the nature of God, showing His Visva Rupa or Universal Form. Arjuna is amazed! Devotion to such an unlimited Being naturally develops as he comes to appreciate the glory of God. After revealing so much information to Arjuna, Sri Krsna tells him:
18:64: Because you are exceedingly dear to Me, hear from Me again the most confidential and supreme word which I will declare for your benefit.
18:65: With your mind fixed on Me, be My devotee. Make sacrifice to Me and offer obeisances unto Me; truly you will come to Me. I promise you this because you are dear to Me.
18:66: Abandoning all types of religious and moral duties take refuge in Me alone. I will liberate you from all inauspiciousness; do not grieve.
Sri Krsna thus reveals to Arjuna in a step by step systematic process that devotional service is the highest form of yoga, the most advanced way to know God. By going through the Gita verse by verse one comes to understand why this is so and how this Path can be walked. For those wishing to practice or understand the art of devotional service, the Gita is essential knowledge.
Write back any time,
John of AllFaith
Jagannatha Prakasa