nimittani ca tasyeha
svato jñanam kutah pumsam
bhaktir vairagyam eva va
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Spotless devotees of the Lord have mentioned the source of such knowledge. How could one have knowledge of devotional service and detachment without the help of such devotees?
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
There are many inexperienced persons who advocate self-realization without the help of a spiritual master. They decry the necessity of the spiritual master and try themselves to take his place by propagating the theory that a spiritual master is not necessary. Srimad-Bhagavatam, however, does not approve this viewpoint. Even the great transcendental scholar Vyasadeva had need of a spiritual master, and under the instruction of his spiritual master, Narada, he prepared this sublime literature, Srimad-Bhagavatam. Even Lord Caitanya, although He is Krsna Himself, accepted a spiritual master; even Lord Krsna accepted a spiritual master, Sandipani Muni, in order to be enlightened; and all the acaryas and saints of the world had spiritual masters. In Bhagavad-gita Arjuna accepted Lord Krsna as his spiritual master, although there was no necessity of such a formal declaration. So, in all cases, there is no question about the necessity of accepting a spiritual master. The only stipulation is that the spiritual master should be bona fide; i.e., the spiritual master must be in the proper chain of disciplic succession, called the parampara system.
Suris are great scholars, but they may not always be anagha, or spotless. The anagha-suri is one who is a pure devotee of the Lord. Those who are not pure devotees of the Lord, or who want to be on an equal level with Him, are not anagha-suri. Pure devotees have prepared many books of knowledge on the basis of authorized scriptures. Srila Rupa Gosvami and his assistants, under the instructions of Lord Sri Caitanya Mahaprabhu, have all written various literatures for the guidance of prospective devotees, and anyone who is very serious about raising himself to the standard of a pure devotee of the Lord must take advantage of those literatures.