The subject about the relationship between God and devotee is of two types:
In Nivrutti, the devotee serves God practically with full knowledge and climax of devotion without aspiring for any fruit in return. This type of devotion is almost practically impossible in this world and is applicable hardly to one or two devotees
, that too, after strenuous spiritual effort for millions of births as said in the Gita (Kashchitmaam, bahunaamjanmanaam)
In Pravrutti, the devotion means only for fruit in return from God. Almost all the world is based on this devotion only. If the aspiration of fruit is deleted, there will be no concept of God at all in this world and I very surely tell all of you that all the human beings in this world become only perfect atheists! There is a saying that even a fool does not spend his/her time or energy or money uselessly without aspiring for the fruit in return (Prayojanamanuddishyanamandopipravartate…). Therefore, the devotees of Nivrutti-type are not even fools but deserve to be placed in higher state than foolishness. Hence, Nivrutti is said to be madness for God and its climax. Certainly, a mad person does such mad activities like spending time, energy and money for the work of God without aspiration for the fruit in return.
Source - http://www.universal-spirituality.org/msg30072016.html