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 sub-headings 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, still whatever I have done will not be lost. In my next life, from the very point where I stopped 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 advance in devotional service. Anyway, for persons who have a natural taste for understanding books like the Bhagavad-gītā and Śrīmad-Bhāgavatam, devotional service is easier than for those who are simply accustomed to mental speculation and argumentative processes.
To support this statement there are many authoritative assertions by the learned scholars of bygone ages. According to their general opinion, a person may become governed by certain convictions derived by his own arguments and decisions. Then another person, who may be a greater logician, will nullify these conclusions and establish another thesis. In this way the path of argument will never be safe or conclusive. The Śrīmad-Bhāgavatam recommends, therefore, that one follow in the footsteps of the authorities.
Here is a general description of devotional service given by Śrī Rūpa Gosvāmī in his Bhakti-rasāmṛta-sindhu. Previously, it has been stated that devotional service can be divided into three categories—namely, devotional service in practice, devotional service in ecstasy, and devotional service in pure love of God. Now Śrī Rūpa Gosvāmī proposes to describe devotional service in practice.
Practice means employing our senses in some particular type of work. Therefore devotional service in practice means utilizing our different sensory organs in service to Kṛṣṇa. Some of the senses are meant for acquiring knowledge, and some are meant for executing the conclusions of our thinking, feeling and willing. So practice means employing both the mind and the senses in practical devotional service. This practice is not for developing something artificial. For example, a child learns or practices to walk. This walking is not unnatural. The walking capacity is there originally in the child, and simply by a little practice he walks very nicely. Similarly, devotional service to the Supreme Lord is the natural instinct of every living entity. Even uncivilized men like the aborigines offer their respectful obeisances to something wonderful exhibited by nature's law, and they appreciate that behind some wonderful exhibition or action there is something supreme. So this consciousness, though lying dormant in those who are materially contaminated, is found in every living entity. And, when purified, this is called Kṛṣṇa consciousness.