"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. Śrīmad-Bhāgavatam, however, does not approve this viewpoint. Even the great transcendental scholar Vyāsadeva had need of a spiritual master, and under the instruction of his spiritual master, Nārada, he prepared this sublime literature, Śrīmad-Bhāgavatam. Even Lord Caitanya, although He is Kṛṣṇa Himself, accepted a spiritual master; even Lord Kṛṣṇa accepted a spiritual master, Sāndīpani Muni, in order to be enlightened; and all the ācāryas and saints of the world had spiritual masters. In Bhagavad-gītā Arjuna accepted Lord Kṛṣṇa 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 paramparā system.
Sūris are great scholars, but they may not always be anagha, or spotless. The anagha-sūri 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-sūri. Pure devotees have prepared many books of knowledge on the basis of authorized scriptures. Śrīla Rūpa Gosvāmī and his assistants, under the instructions of Lord Śrī Caitanya Mahāprabhu, 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."
(Śrīmad-Bhāgavatam 3.7.39, Purport)