An ideal devotee serves and pleases Krishna to the highest degree, gratifying His transcendental senses and desires. As Krishna is the supreme enjoyer, satisfying His desires is the way He relishes rasa or relationships. When He relishes that rasa with those who give pleasure to Him without any expectation of getting pleasure in return, then such devotees experience bliss, which is one of the byproducts of devotion.
Lectures from a Disciple, "Serving a Person", Pg 51, 2nd Paragraph