How you can have full knowledge if you are so defective? Just like a diseased man. He cannot say, "I am perfect in health." That is not possible. Similarly, if we are defective in so many ways, and if I want to become teacher or preacher to give you the truth, then how can I give? This is not possible. So we cannot hear from anyone who is defective. That is not pure knowledge, that is not perfect knowledge.
Lecture on Bhagavad-gita 7.1 -- London, March 9, 1975