Bhagavad-gītā is also known as Gītopaniṣad. It is the essence of Vedic knowledge and one of the most important Upaniṣads in Vedic literature. Of course there are many commentaries in English on the Bhagavad-gītā, and one may question the necessity for another one. This present edition can be explained in the following way. Recently an American lady asked me to recommend an English translation of Bhagavad-gītā. Of course in America there are so many editions of Bhagavad-gītā available in English, but as far as I have seen, not only in America but also in India, none of them can be strictly said to be authoritative because in almost every one of them the commentator has expressed his own opinions without touching the spirit of Bhagavad-gītā as it is.
The spirit of Bhagavad-gītā is mentioned in Bhagavad-gītā itself. It is just like this: if we want to take a particular medicine, then we have to follow the directions written on the label. We cannot take the medicine according to our own whim or the direction of a friend. It must be taken according to the directions on the label or the directions given by a physician. Similarly, Bhagavad-gītā should be taken or accepted as it is directed by the speaker himself. The speaker of Bhagavad-gītā is Lord Śrī Kṛṣṇa. He is mentioned on every page of Bhagavad-gītā as the Supreme Personality of Godhead, Bhagavān. Of course the word “bhagavān” sometimes refers to any powerful person or any powerful demigod, and certainly here Bhagavān designates Lord Śrī Kṛṣṇa as a great personality, but at the same time we should know that Lord Śrī Kṛṣṇa is the Supreme Personality of Godhead, as is confirmed by all great ācāryas (spiritual masters) like Śaṅkarācārya, Rāmānujācārya, Madhvācārya, Nimbārka Svāmī, Śrī Caitanya Mahāprabhu and many other authorities of Vedic knowledge in India. The Lord Himself also establishes Himself as the Supreme Personality of Godhead in the Bhagavad-gītā, and He is accepted as such in the Brahma-saṁhitā and all the Purāṇas, especially the Śrīmad-Bhāgavatam, known as the Bhāgavata Purāṇa (Kṛṣṇas tu bhagavān svayam). Therefore we should take Bhagavad-gītā as it is directed by the Personality of Godhead Himself.
In the Fourth Chapter of the Gītā the Lord says:
Here the Lord informs Arjuna that this system of yoga, the Bhagavad-gītā, was first spoken to the sun-god, and the sun-god explained it to Manu, and Manu explained it to Ikṣvāku, and in that way, by disciplic succession, one speaker after another, this yoga system has been coming down. But in the course of time it has become lost. Consequently the Lord has to speak it again, this time to Arjuna on the Battlefield of Kurukṣetra.