A musician, because one has got a good attachment for music, tries to perform it very perfectly. So love is the basis. Similarly, when you serve Krsna, if you have no love for Krsna, you cannot serve Him very nicely. And Krsna also does not accept your service if it is not done in great love and affection.
From Srila Prabhupada’s lecture on Bhagavad-gita 2.39 — 12 September, 1973