We have nothing to offer Krishna because He is the Proprietor of everything that be. But when He sees that a living entity is trying to serve Him, that is appreciated. In Bhagavad-gita you have seen that Krishna says to offer Him a leaf, a fruit, a flower or even some water. Actually, the Supreme Lord has no necessity to request us to offer Him these items or any other items; but He gives us the opportunity of serving Him so that we may become qualified to enter back to Home, back to Godhead.
Letter to Carl Lange, 14 November, 1969