A seven-hundred verse record of a conversation between Lord Kṛṣṇa and His disciple, Arjuna, from the Bhīṣma Parva of the Mahābhārata of Vedavyāsa. The conversation took place between two armies minutes before the start of an immense fratricidal battle. Kṛṣṇa teaches the science of the Absolute Truth and the importance of devotional service to the despondent Arjuna, and it contains the essence of all Vedic wisdom.
Śrīla Prabhupāda’s annotated English translation is called Bhagavad-gītā As It Is; This most essential text of spiritual knowledge, The Song of the Lord, contains Kṛṣṇa’s instructions to Arjuna at Kurukṣetra. It is found in the Mahābhārata. The Mahābhārata is classified as smṛti-śāstra, a supplement of the śruti-śāstra. Śruti, the core Vedic literature, includes the four Vedas (Ṛg, Sāma, Yajur and Atharva) and the Upaniṣads.
Śruti advances the understanding of the absolute. Bhagavad-gītā is also known as Gītopaniṣad, or a śruti text spoken by the Supreme Personality of Godhead Himself. Therefore, Śrīla Pra-bhupāda wrote in a letter, the Gītā should be taken as śruti. But they take it as smṛti because it is part of the smṛti (Mahābhārata).
In one sense it is both śruti and smṛti. In only 700 verses, the Bhagavad-gītā summarizes all Vedic knowledge about the soul, God, sanātana-dharma, sacrifice, yoga, karma, reincarnation, the modes of material nature, Vedānta and pure devotion.