Just the other day I was reading Brhad Bhagavatamrta. In volume 1, chapter 7, Krishna told Satyabhama, "I can never fully repay these devotees [the Vrajavasis], and so I am utterly indebted to them." In the commentary, Sanatana Goswami says that since Krishna cannot repay His debt of gratitude, He constantly looks for small favors He can do for them as a token of His affection. Krishna shows by His example the ways to reciprocate love. Though we cannot imitate Krishna, still, if He looks for small favors as tokens of His affection to those who serve Him, then certainly we should try to do the same.
Collected Letters to Friends and disciples Vol 5, Pg 58, 2nd paragraph.