There are three basic methods of obtaining knowledge, two of which are faulty, and one which is faultless when properly applied. The two faulty methods are: 1. Direct perception, and 2. Induction (making general conclusions from limited experience). The faultless method is the descending process by which one hears from the proper authority who is faultless (Krishna or His pure devotees).
The two faulty methods are known as the "ascending process." "Ascending" means to go up. So one who follows these processes is trying to understand God or Truth with his limited faulty faculties. We see the adherents of these methods changing their theories constantly. They are not sure of anything.
In Krishna consciousness we hear Krishna’s opinion which is perfect, because He is omniscient; that is, there is nothing unknown to Him. His words are always perfect and true. There is no need of a new opinion every 5 minutes. Krishna’s devotees who are in the disciplic succession simply repeat His words and therefore what they speak is also perfect.
Srila Prabhupada gave the example of a small boy who asks his father what is the name of the object into which his father is speaking. His father replies, "microphone." The boy repeats. Even though the boy may not have complete understanding, because he is repeating what is true, his words are true.
Revelation, not speculation, is the only way one can understand God. Krishna wants us to know Him, so He reveals Himself through the scriptures and His pure devotees.
The Vedas tell us that if one wants to make advancement in spiritual life it is imperative to accept a spiritual master.’ In any discipline we need a teacher. Book learning is not sufficient. For example, a surgeon must study under an expert experienced surgeon. He cannot confine his learning to books. One who does not accept a bonafide. Spiritual master as his guide is sure to be bewildered in his attempts at self-realization.
One must be extremely careful in choosing a spiritual master, as there are many pretenders who simply wish to cheat innocent persons. There are standards mentioned in the Vedic literature that one should use when picking one’s eternal guide: 1. The spiritual master must come in an unbroken chain of disciplic succession from God Himself, 2. The spiritual master must be a perfect disciple of his spiritual master; a first class servant rendering humble service, 3. The spiritual master must be fixed in the regulative principles and practices of Krishna consciousness, never falling down, 4. The spiritual master must haveheard nicely from his spiritual master so that he is simply repeating in his own words the teachings given to him.
The spiritual master teaches by example as well as precept. By observing his behavior, the prospective disciple can verify that the spiritual master is not deviating from the teachings that he received from his own spiritual master and is, in turn, passing along to his disciples. In this way,the disciple can understand how to apply the teachings to his own life.
1. Mundaka Upanisad 1.2.12