One should become submissive, jnane prayasam udapasya namanta eva, that very submissive to hear from the right person. So hearing is so important. Therefore our all Vedic literature is called sruti. So the subject matter which is beyond our sense perception, avan manasa gocara, that cannot be understood by using our imperfect senses. Now the question is: from whom to hear? So in the sastra it is said, san-mukharitam: "You have to hear from realized saintly person." It is said in the Bhagavad-gita, tad viddhi pranipatena pariprasnena sevaya, upadeksyanti tad jnanam jnaninas tattva-darsinah. You have to hear from a person who has seen or who has understood the Absolute Truth and who is tat, sad-guru.

(S.B. Lec. 6.1.15 Nellore 8th January, 1976)