Lord Kṛṣṇa spoke the Bhagavad-gītā to His friend and devotee Arjuna on the battlefield of Kurukshetra just before the onset of war. The purpose of Bhagavad-gītā is to deliver mankind from the nescience of material existence. Bhagavad-gītā is also known as Gītopaniṣad. It is the essence of Vedic knowledge and one of the most important Upaniṣads in Vedic literature. His Divine Grace A.C. Bhaktivedanta Swami Prabhupada translated and commented on the transcendental literature Bhagavad-gītā.
You may go through the verses [original Sanskrit text and its English transliteration] and purports of the Bhagavad-gītā at the following link:
https://vedabase.io/en/library/bg
Because Bhagavad-gītā is spoken by the Supreme Personality of Godhead, one need not read any other Vedic literature. One need only attentively and regularly hear and read Bhagavad-gītā. This one book, Bhagavad-gītā, will suffice, because it is the essence of all Vedic literatures and especially because it is spoken by the Supreme Personality of Godhead. (Gītā-māhātmya 4)
sarvopaniṣado gāvo dogdhā gopāla-nandanaḥ pārtho vatsaḥ su-dhīr bhoktā dugdhaṁ gītāmṛtaṁ mahat
“This Gītopaniṣad, Bhagavad-gītā, the essence of all the Upaniṣads, is just like a cow, and Lord Kṛṣṇa, who is famous as a cowherd boy, is milking this cow. Arjuna is just like a calf, and learned scholars and pure devotees are to drink the nectarean milk of Bhagavad-gītā.” (Gītā-māhātmya 6)
