BG Chap 18 - Bhakti and niṣkāma-karma
Niṣkāma-karma purifies the heart, and in proportion to the purification of the heart there will be an awakening of knowledge. Therefore, for awakening knowledge even the sannyāsīs must perform niṣkāma-karma-yoga. But one who attains complete purification of heart need no longer perform karma. And bhakti, being independent, supreme and most powerful, does not rely on purification of the heart. Although knowing that following the principles of dharma has good qualities like purification, and also knowing the sin of not following dharma, a devotee gives up these practices with the firm conviction that just by being a devotee all will be accomplished, as these other things cause distraction to meditation upon Kṛṣṇa. Supreme bhakti enters from the very beginning of practice into a person afflicted with material diseases, and removes lust and other impurities. In the Bhāgavatam it is said that the sound incarnation of Kṛṣṇa enters into the heart, sits on the lotus flower of his loving relationship, and cleanses the dust of material association. Since bhakti purifies the heart in such a way, a devotee need not perform prescribed duties.