In this purport, Srila Prabhupada described the Bhakti-sandarbha in these words: The fifth Sandarbha is called Bhakti-sandarbha, and in this book there is a discussion of how devotional service can be directly executed, and how such service can be adjusted, either directly indirectly.
In the course of this discussion it is emphatically and repeatedly explained that devotional service to the Lord must be executed under the direction of a bona fide spiritual master. The qualifications of such a spiritual master are discussed at great length and indeed, association with such an advance devotee is explained as the actual cause of engagement in devotional service.