The speaker of the Bhagavad-gītā is Lord Śrī Kṛṣṇa. He is mentioned in every page of the Bhagavad-gītā as the Supreme Personality of Godhead, Bhagavān. Of course, "bhagavān" is sometimes designated to any powerful person or any powerful demigod, but here bhagavān is certainly designated to Śrī Kṛṣṇa, a great personality, but at the same time we must know that Lord Śrī Kṛṣṇa, as He is confirmed by all the ācāryas... I mean to say, even Śaṅkarācārya, Rāmānujācārya, Madhvācārya, Nimbārka Svāmī and Śrī Caitanya Mahāprabhu and many others. In India there were many authoritative scholars and ācāryas, I mean, authorities of the Vedic knowledge. All of them, including Śaṅkarācārya, has accepted Śrī Kṛṣṇa as the Supreme Personality of Godhead. The Lord Himself has also established Himself as the Supreme Personality of Godhead in the Bhagavad-gītā. He is accepted so in the Brahmā-saṁhitā and all Purāṇas, especially in the Bhāgavata Purāṇa: kṛṣṇas tu bhagavān svayam (SB 1.3.28). So therefore we should take Bhagavad-gītā as it is directed by the Personality of Godhead Himself.
So in the Fourth Chapter of Bhagavad-gītā the Lord says,
- imaṁ vivasvate yogaṁ
- proktavān aham avyayam
- vivasvān manave prāha
- manur ikṣvākave 'bravīt
- (BG 4.1)
- evaṁ paramparā-prāptam
- imaṁ rājarṣayo viduḥ
- sa kāleneha mahatā
- yogo naṣṭaḥ parantapa
- (BG 4.2)
- sa evāyaṁ mayā te 'dya
- yogaḥ proktaḥ purātanaḥ
- bhakto 'si me sakhā ceti
- rahasyaṁ hy etad uttamam
- (BG 4.3)
The idea is... The Lord said to Arjuna that "This yoga, this system of yoga, Bhagavad-gītā, was first spoken by Me to the sun-god and the sun-god explained to Manu. Manu explained to Ikṣvāku, and in that way, by disciplic succession, one after another, this yoga system is coming, and in course of time this system is now lost. And therefore, I am speaking to you the very same yoga system again, the very same old yoga system of Bhagavad-gītā, or Gītopaniṣad. Because you are My devotee and you are My friend, therefore it is possible for you only to understand."
Now the purport is that Bhagavad-gītā is a treatise which is specially meant for the devotee of the Lord. There are three classes of transcendentalists, namely the jñānī, the yogī and the bhakta. Or the impersonalist, or the meditator, or the devotees. So here it is clearly mentioned. The Lord says to Arjuna that "I am speaking or I am making you the first man of the paramparā. Because the old paramparā or disciplic succession is now broken, therefore I wish to establish again another paramparā in the same line of thought as it was coming down from the sun-god to others. So you, you take it and you distribute it. Or the system, the yoga system of Bhagavad-gītā may now be distributed through you. You become the authority of understanding Bhagavad-gītā." Now here is a direction that Bhagavad-gītā is especially instructed to Arjuna, the devotee of the Lord, the direct student of Kṛṣṇa. And not only that, he is intimately in touch with Kṛṣṇa as friend. Therefore Bhagavad-gītā is understood by a person who has similar qualities like Kṛṣṇa. That means he must be a devotee, he must be in relation, direct relationship with the Lord.