The three categories of devotional service which Śrīla Rūpa Gosvāmī describes in Bhakti-rasāmṛta-sindhu are listed as devotional service in practice, devotional service in ecstasy and devotional service in pure love of Godhead. There are many subheadings in each of these categories. Generally it is understood that in the category of devotional service in practice there are two different qualities, devotional service in ecstasy has four qualities, and devotional service in pure love of Godhead has six qualities. These qualities will be explained by Śrīla Rūpa Gosvāmī later on.
In this connection, Śrīla Rūpa Gosvāmī suggests that the person eligible for Kṛṣṇa consciousness, or devotional service, can be classified by his particular taste. He says that devotional service is a continual process from one's previous life. No one can take to devotional service unless he has had some previous connection with it. For example, suppose in this life I practice devotional service to some extent. Even though it is not one-hundred-percent perfectly performed, whatever I have done will not be lost. In my next life, from the very point where I stop in this life, I shall begin again. In this way there is always a continuity. But even if there is no continuity, if only by chance a person takes interest in a pure devotee's instruction, he can be accepted and can advance in devotional service. Anyway, for persons who have a natural taste for understanding books like Bhagavad-gītā and Śrīmad-Bhāgavatam, devotional service is easier than for those who are simply accustomed to mental speculation and argumentative processes.