Guru means he should give evidences from śāstra. So we must select guru.
Lecture on BG 2.1-11 -- Johannesburg, October 17, 1975: Nowadays it has become a fashion; everyone is becoming guru and he is giving his own opinion, "I think," "In my opinion." That is not guru. Guru means he should give evidences from śāstra. Yaḥ śāstra-vidhim utsṛjya vartate kāma-kārataḥ: [Bg. 16.23] "Anyone who does not give evidences, proof, from the śāstra, then" na siddhiṁ sa avāpnoti, "he does not get at any time success," na sukham, "neither any happiness in this material world," na parāṁ gatim, "and what to speak of elevation in the next life." These are the injunction.
So we must select guru. Here it is, example, Arjuna. He's accepting Kṛṣṇa as guru. Why he is accepting? Because, he says,
- na hi prapaśyāmi mamāpanudyād
- yac chokam ucchoṣaṇam indriyāṇām
- avāpya bhūmāv asapatnam ṛddhaṁ
- rājyaṁ surāṇām api cādhipatyam
[Bg. 2.8]
So he has selected that the right person, guru, and he said that "Unless I hear from You what is right and wrong, I cannot decide whether I shall fight or I shall not fight. Which way is better for me I cannot understand."