In the Caitanya-caritāmṛta three kinds of devotional service are described-namely, bhakti (ordinary devotional service), śuddha-bhakti (pure devotional service) and viddha-bhakti (mixed devotional service).
When devotional service is executed with some material purpose, involving fruitive activities, mental speculations or mystic yoga, it is called mixed or adulterated devotional service. Besides bhakti-yoga, the Bhagavad-gītā also describes karma-yoga, jñāna-yoga and dhyāna-yoga. Yoga means linking with the Supreme Lord, which is possible only through devotion. Fruitive activities ending in devotional service, philosophical speculation ending in devotional service, and the practice of mysticism ending in devotional service are known respectively as karma-yoga, jñāna-yoga and dhyāna-yoga. But such devotional service is adulterated by the three kinds of material activities.
For those grossly engaged in identifying the body as the self, pious activity, or karma-yoga, is recommended. For those who identify the mind with the self, philosophical speculation, or jñāna-yoga, is recommended. But devotees standing on the spiritual platform have no need of such material conceptions of adulterated devotion. Adulterated devotional service does not directly aim for love of the Supreme Personality of Godhead. Therefore service performed strictly in conformity with the revealed scriptures is better than such viddha-bhakti because it is free from all kinds of material contamination. It is executed in Kṛṣṇa consciousness, solely to please the Supreme Personality of Godhead.
Those who are spontaneously devoted to the Lord and have no aims for material gain are called attracted devotees. They are spontaneously attracted to the service of the Lord, and they follow in the footsteps of self-realized souls.
Ref >> Srila Prabhupada Vani.