The root cause of devotional service to Lord Krishna is association with advanced devotees. Even when one's dormant love for Krishna awakens, association with devotees is still most essential.
The more, progress is made in devotional service under the guidance of the Bhagavatas, the more one becomes fixed in the transcendental loving service of the Lord. The messages of the book Bhagavata, therefore, has to be received from the devotee Bhagavata and the combination of these two Bhagavatas will help the neophyte devotee to make progress.
Constant engagement in devotional service can be performed only when one is working under the direction of a bona fide spiritual master. The Vedic injunction is that no one can have full knowledge without being under the guidance of an Acarya.
If after accepting the spiritual master and being initiated one does not follow the rules and regulations of devotional service, then he is again fallen.
One must execute devotional service under the guidance of a devotee or directly under the guidance of the Supreme Personality of Godhead. It is not possible, however, to train oneself without guidance from the spiritual master.
By the slow process of devotional service, under the guidance of the bona fide spiritual master, one can attain the highest stage.