Bhagavad-gītā is the science of God, the spiritual science. But it was being adulterated by so many grains of sands. So people could not understand it. We do not present Bhagavad-gītā with some adulteration. Kṛṣṇa says, bhakto 'si priyo 'si arjuna. Kṛṣṇa is instructing Arjuna to begin the paramparā system, because the paramparā system was supposed to be broken. People misunderstood. Or some way or other, it was broken, as it is going on now also.
So Kṛṣṇa said that, "I shall speak to you this same old philosophy of Bhagavad-gītā again." "Why unto me?" Why Kṛṣṇa selected Arjuna? There are many others, learned scholars. Now, Kṛṣṇa says, bhakto 'si priyo 'si. Kṛṣṇa was a military man . . . er, Arjuna was a military man. He was not a Vedāntist. He was a gṛhastha, not even a sannyāsī. Why Kṛṣṇa selected to instruct Arjuna as the disciple of the renovated paramparā system? That is also spoken by Kṛṣṇa: bhakto 'si priyo 'si (BG 4.3), rahasyam etad uttamam, "Because you are My dear friend, because you are My devotee, you can understand the mysteries of Bhagavad-gītā."
Kṛṣṇa did not select a so-called Vedāntist to understand Bhagavad-gītā. Because Arjuna was not a Vedāntist; he was a military man. He's not supposed to become a great philosopher. He was a gṛhastha. But the real qualification is to become a devotee of Kṛṣṇa. Then one can understand what is Bhagavad-gītā. Not by so-called knowledge. No. Knowledge is not perfect unless one understands Kṛṣṇa. That is not knowledge, that is still illusion.
Therefore in the Bhagavad-gītā it is said, bahūnāṁ janmanām ante jñānavān māṁ prapadyate (BG 7.19). Māṁ prapadyate: "He surrenders unto Me." Vāsudevaḥ sarvam iti sa mahātmā sudurlabhaḥ. When one understands Kṛṣṇa, Vāsudeva, as everything, as the origin of everything, janmādy asya yataḥ (SB 1.1.1), then his knowledge is perfect. And so long he's hovering here and there, without any understanding of Kṛṣṇa, his knowledge is not perfect. That perfection of knowledge is attained, as it is described by Kṛṣṇa: bahūnāṁ janmanām ante (BG 7.19).