Serving a person is the essence of devotion. Therefore, the impersonalists cannot have devotion. It is very difficult to be devoted to an inanimate object or to an impersonal void. Where is the quality or characteristic of devotion for an entity that has no life, no desires and no personality? When referring to service, Srila Prabhupada refers to it as devotional service to enhance its real meaning. There is no question of service to God without devotion. Bhakti is therefore translated as devotional service.
Lectures from a Disciple, "Serving a Person", Pg 51, 1st Paragraph