Bhakti-yoga is the purification of the senses. At the present moment in material existence the senses are always impure, being engaged in sense gratification. But by the practice of bhakti-yoga these senses can become purified, and in the purified state they come directly in contact with the Supreme Lord. In this material existence, I may be engaged in some service to some master, but I don't really lovingly serve my master. I simply serve to get some money. And the master also is not in love; he takes service from me and pays me. So there is no question of love. But for spiritual life, one must be elevated to the pure stage of love. That stage of love can be achieved by practice of devotional service, performed with the present senses.
(Bhagavad-Gita--------12:9-------purport).

The senses in the material world are surcharged with material ignorance. In every way, the authorities have recommended purification of the senses from the material conception. In the material world the senses are manipulated for individual and personal satisfaction, whereas in the spiritual world the senses are properly used for the purpose for which they were originally meant, namely the satisfaction of the Supreme Lord. Such sensual activities are natural, and therefore sense gratification there is uninterrupted and unbroken by material contamination because the senses are spiritually purified. And such satisfaction of the senses is equally shared by the transcendental reciprocators. Since the activities are unlimited and constantly increasing, there is no scope for material attempts or artificial arrangements.
(Srimad Bhagavatam------2:7:47--------purport).