The definition of a pure devotee, as given by Rūpa Gosvāmī in Bhakti-rasāmṛta-sindhu, can be summarized thus: his service is favorable and is always in relation to Kṛṣṇa. In order to keep the purity of such Kṛṣṇa conscious activities, one must be freed from all material desires and philosophical speculation. Any desire except for the service of the Lord is called material desire. And philosophical speculation refers to the sort of speculation which ultimately arrives at a conclusion of voidism or impersonalism. This conclusion is useless for a Kṛṣṇa conscious person. Only rarely by philosophical speculation can one reach the conclusion of worshiping Vāsudeva, Kṛṣṇa. This is confirmed in the Bhagavad-gītā itself. The ultimate end of philosophical speculation, then, must be Kṛṣṇa, with the understanding that Kṛṣṇa is everything, the cause of all causes, and that one should therefore surrender unto Him. If this ultimate goal is reached, then philosophical advancement is favorable, but if the conclusion of philosophical speculation is voidism or impersonalism, that is not bhakti.
Karma or fruitive activities are sometimes understood to be ritualistic activities. There are many persons who are very much attracted by the ritualistic activities described in the Vedas. But if one becomes attracted simply to ritualistic activities without understanding Kṛṣṇa, his activities are unfavorable to Kṛṣṇa consciousness. Actually, Kṛṣṇa consciousness can be based simply on hearing, chanting, remembering, etc. Described in the Śrīmad-Bhāgavatam are nine different processes, besides which everything done is unfavorable to Kṛṣṇa consciousness. Thus, one should always be guarding against falldowns.
Śrīla Rūpa Gosvāmī has also mentioned in this definition of bhakti the word jñāna-karmādi. This karmādi (fruitive work) consists of activities which are unable to help one attain to pure devotional service. Many forms of so-called renunciation are also not favorable to Kṛṣṇa conscious devotional service.
Śrīla Rūpa Gosvāmī has also quoted a definition from the Nārada-pañcarātra, as follows: "One should be free from all material designations and must be cleansed of all material contamination by Kṛṣṇa consciousness. He should be restored to his pure identity, where he engages his senses in the service of the proprietor of the senses." So when our senses are engaged for the actual proprietor of the senses, that is called devotional service. In our conditional state, our senses are engaged in serving these bodily demands. When the same senses are engaged in executing the order of Kṛṣṇa, it is called bhakti.
As long as one identifies himself as belonging to a certain family, a certain society or a certain person, he is said to be covered with designations. When one is fully aware that he does not belong to any family, society or country, but is eternally related to Kṛṣṇa, he then realizes that his energy should be employed not in the interests of so-called family, society or country, but in the interests of Kṛṣṇa. This is purity of purpose and the platform of pure devotional service in Kṛṣṇa consciousness.