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SB 1.2.7

vāsudeve bhagavati
 bhakti-yogaḥ prayojitaḥ
janayaty āśu vairāgyaṁ
 jñānaṁ ca yad ahaitukam
Synonyms: 
vāsudeve — unto Kṛṣṇa; bhagavati — unto the Personality of Godhead; bhakti-yogaḥ — contact of devotional service; prayojitaḥ — being applied; janayati — does produce; āśu — very soon; vairāgyam — detachment; jñānam — knowledge; ca — and; yat — that which; ahaitukam — causeless.
Translation: 
By rendering devotional service unto the Personality of Godhead, Śrī Kṛṣṇa, one immediately acquires causeless knowledge and detachment from the world.
Purport: 

Those who consider devotional service to the Supreme Lord Śrī Kṛṣṇa to be something like material emotional affairs may argue that in the revealed scriptures, sacrifice, charity, austerity, knowledge, mystic powers and similar other processes of transcendental realization are recommended. According to them, bhakti, or the devotional service of the Lord, is meant for those who cannot perform the high-grade activities. Generally it is said that the bhakti cult is meant for the śūdras, vaiśyas and the less intelligent woman class. But that is not the actual fact. The bhakti cult is the topmost of all transcendental activities, and therefore it is simultaneously sublime and easy. It is sublime for the pure devotees who are serious about getting in contact with the Supreme Lord, and it is easy for the neophytes who are just on the threshold of the house of bhakti. To achieve the contact of the Supreme Personality of Godhead, Śrī Kṛṣṇa, is a great science, and it is open for all living beings, including the śūdras, vaiśyas, women and even those lower than the lowborn śūdras, so what to speak of the high-class men like the qualified brāhmaṇas and the great self-realized kings. The other high-grade activities designated as sacrifice, charity, austerity, etc., are all corollary factors following the pure and scientific bhakti cult.

The principles of knowledge and detachment are two important factors on the path of transcendental realization. The whole spiritual process leads to perfect knowledge of everything material and spiritual, and the results of such perfect knowledge are that one becomes detached from material affection and becomes attached to spiritual activities. Becoming detached from material things does not mean becoming inert altogether, as men with a poor fund of knowledge think. Naiṣkarma means not undertaking activities that will produce good or bad effects. Negation does not mean negation of the positive. Negation of the nonessentials does not mean negation of the essential. Similarly, detachment from material forms does not mean nullifying the positive form. The bhakti cult is meant for realization of the positive form. When the positive form is realized, the negative forms are automatically eliminated. Therefore, with the development of the bhakti cult, with the application of positive service to the positive form, one naturally becomes detached from inferior things, and he becomes attached to superior things. Similarly, the bhakti cult, being the supermost occupation of the living being, leads him out of material sense enjoyment. That is the sign of a pure devotee. He is not a fool, nor is he engaged in the inferior energies, nor does he have material values. This is not possible by dry reasoning. It actually happens by the grace of the Almighty. In conclusion, one who is a pure devotee has all other good qualities, namely knowledge, detachment, etc., but one who has only knowledge or detachment is not necessarily well acquainted with the principles of the bhakti cult. Bhakti is the supermost occupation of the human being.