"So long we are imperfect, we cannot give perfect knowledge. Therefore we must find out knowledge from the perfect person. That is Vedic injunction. Tad-vijñānārthaṁ sa gurum eva abhigacchet (MU 1.2.12). Guru, guru means one who has got perfect knowledge. One who hasn't got perfect knowledge, he cannot become guru. How he can? Guru means heavy. So if I am light and I take knowledge from another light person, then what is the use of such knowledge?"
(Srila Prabhupada Lecture, Hyderabad, April 19, 1974)