(Srila Prabhupada taking darshan of Krishna-Balarama, Vrindavan)
"If you want to know God, then you have to go to a person who knows God. You might have gone to a person who does not know. That is another thing. You went to a wrong person. But actually if you want to know God, you must have to go to a person who knows God. That you have to search out. That requires intelligence. But you cannot give up the idea. Because you have been cheated, 'I could not get information'; therefore, you cannot give up that business. You have to find out somebody else. But because you say 'I have been cheated. I could not get the right information. I stop this business,' that is not allowed. You must. Therefore, according to Vedic order it is said, tad vijñānārthaṁ sa gurum evābhigacchet (MU 1.2.12). Abhigacchet means you must go to a person to understand that science of God. You must go to a guru or a man who knows. Guru means who is more intelligent. Guru means weight, heavy, heavier, heavier in knowledge. So you have to find out a person who is heavier than you, not ordinary. Must go. Not that may go or may not go. No. Must go. Tad vijñānārthaṁ sa gurum eva abhigacchet.
And what is the symptom of guru? Śrotriyaṁ. Means he has heard about God from his superior, his guru. Śrotriyaṁ. And how can I know that he has heard from his superior about God? He might say that 'Yes, I have heard,' but what symptoms? Brahma-niṣṭham. Brahma-niṣṭham means that he has become a complete devotee of God, result. Just like a man, physician. A physician means he has attended the medical college, passed the examination, and the result is that he's practicing as a physician. Not only passing will do, but he's actually passing and he's actually practicing and he's curing patients. Therefore, you find out a physician, here is a physician. It is not difficult. So guru means one who knows God. How can I know that he knows God? Because he's making others to know God. Where is the difficulty?"
(Srila Prabhupada Conversation, Los Angeles, June 14, 1972)