Ācārya means one who is speaking exactly the same instruction as Kṛṣṇa has given. That is ācārya. Not ācārya . . . everyone becomes ācārya, "In my opinion it is like . . ." Who are you? If you have got any opinion, then you write your own book. Why do you touch Bhagavad-gītā? Because Bhagavad-gītā is very well known book all over the world, these rascals take advantage of Bhagavad-gītā and interpret it in their own way. That is not ācārya. Ācārya means, as Kṛṣṇa says that, "Millions of years ago I spoke this Bhagavad-gītā . . ." Imaṁ vivasvate yogaṁ proktavān aham avyayam, vivasvān (BG 4.1). "I spoke to the sun-god millions and millions of years ago." Vivasvān manave prāha manur ikṣvākave 'bravīt. Manu . . . If you simply calculate the age of Manu, it becomes millions and trillions of years. So before that. Because Vivasvān spoke to Manu. So Manu's age we cannot calculate. Before that.
So this is the paramparā system. Kṛṣṇa said to the sun-god, Vivasvān. Vivasvān exactly transferred the message to Manu. Manu transferred the message to Mahārāja Ikṣvāku. Mahārāja Ikṣvāku is the first king of the sun dynasty, sūrya-vaṁśa, kṣatriya, the forefather of the dynasty where Rāmacandra, Lord Rāmacandra, appeared. So the . . . that is ācārya. So we have to accept. At the present moment the ācārya, Kṛṣṇa, is instructing Arjuna. So Arjuna is ācārya.