So according to Vedic system, one has to accept a spiritual master in order to make a solution of his life. In every step of his life the spiritual master guides him. He also makes question to the spiritual master and he guides him so that he will . . . his life, his progress of life, may be systematic.
Now, to take such guidance means the spiritual master should also be a very perfect man. Otherwise, how can he guide? Now, here Arjuna knows that Śrī Kṛṣṇa is the perfect person. So therefore he is accepting Him as śiṣyas te 'haṁ śādhi māṁ tvāṁ prapannam (BG 2.7): "I am just surrendering unto You, You self, Yourself, and You accept me as Your disciple, because friendly talks cannot make a solution of the perplexity." Friendly talks may be going on for years together, but there is no solution. Here, accepting Kṛṣṇa as the spiritual master means whatever Kṛṣṇa will decide, he has to accept.
One cannot deny the order of a spiritual master. Therefore one has to select a spiritual master whose order, carrying, you'll not commit a mistake. You see? Now, suppose if you accept a wrong person as spiritual master, and if you, if he guides you wrongly, then your whole life is spoiled. So one has to accept a spiritual master whose guidance will make his life perfect. That is the relation between spiritual master and disciple. It is not a formality. It is a great responsibility both for the disciple and for the spiritual master.