Any sincere soul who is searching for spiritual science must try to seek out a bona fide spiritual master in disciplic succession (parampara). Lord Sri Kṛṣṇa is the original spiritual master. The Vedic knowledge, as it is, has been handed down from master to disciple, one after another. Even on the mundane platform, if someone wants to learn chemistry, he has to approach a professor of chemistry; how much greater, then, is the need to approach a bona fide spiritual master to attain the supreme spiritual perfection, Kṛṣṇa consciousness. It is absolutely necessary for a sincere soul to approach a bona fide spiritual master and surrender unto the lotus feet of the spiritual master without reservation. Lord Sri Caitanya Mahaprabhu instructed Sanatana Gosvami thus: “The first and foremost thing is that one should accept a bona fide spiritual master. That is the beginning of spiritual life”.
The Personality of Godhead, Sri Kṛṣṇa has said in the Bhagavad-gita that after many births a learned sage surrenders unto Him, and that it is rare to see such a mahatma, who is able to connect everything to Vasudeva (the plenary manifestation of Viṣṇu). Such a mahatma never tries to approach Godhead by any invented method – one concocted through the inductive, ascending process of knowledge. Rather, he accepts the deductive, descending process – that is, the method that comes down directly from the Supreme Lord or through His bona fide representatives. No one can reach the Lord by the ascending process, even after endeavouring for many, many years. All that is obtained by this ascending process is imperfect, partial, impersonal knowledge, which deviates one from the Absolute Truth. By the empiric process of philosophical research, one can perhaps distinguish the metaphysical subjects from the physical objects, but unless the seeker of truth can reach the personal feature of the Absolute Truth, he gains only dry, impersonal knowledge of Him, without any actual transcendental profit.
Source: A.C. Bhaktivedanta Swami Prabhupada (2012 edition), “The Scientific Basis of Krishna Consciousness”, Page 50 A.C. Bhaktivedanta Swami Prabhupada (2012 edition), “Message of Godhead”, Page 38 A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “The Science of Self-Realization”, Page 84