A beautiful verse in the Srimad Bhagavatam explains that one's service to Krishna is not because He needs it, but because the offerer needs it. In the Seventh Canto of Srimad Bhagavatam, Prahlada Maharaja says that:
"The Supreme Lord, the Supreme Personality of Godhead, is always fully satisfied in Himself. Therefore when something is offered to Him, the offering, by the Lord's mercy, is for the benefit of the devotee, for the Lord does not need service from anyone. To give an example, if one's face is decorated, the reflection of one's face in a mirror is also seen to be decorated."