Kṛṣṇa becomes obliged to the loving spirit of the devotee and not exactly to the service rendered. No one can serve Kṛṣṇa completely. He is so complete and self-sufficient that He has no need of any service from the devotee. It is the devotee's attitude of love and affection for Kṛṣṇa that makes Him obliged. A very nice example of this obligatory behavior was manifested when Sudāmā Vipra went to Kṛṣṇa's palace. Sudāmā Vipra had been a class friend of Kṛṣṇa's, and due to his poverty he was induced by his wife to see Kṛṣṇa to request some aid. When Sudāmā Vipra reached Kṛṣṇa's palace, Kṛṣṇa received him very well, and both He and His wife washed the feet of Sudāmā Vipra, showing respect to the brāhmaṇa. Remembering His loving affairs with Sudāmā in their childhood, Kṛṣṇa began to shed tears while receiving him.
Another instance of Kṛṣṇa's obligation to His devotee is described in the Tenth Canto, Ninth Chapter, verse 18, of Śrīmad-Bhāgavatam, where Śukadeva Gosvāmī tells King Parīkṣit, "My dear King, when mother Yaśodā was perspiring, tired of trying to bind Kṛṣṇa up with rope, Kṛṣṇa agreed to allow her to bind Him." Kṛṣṇa, as a child, was disturbing His mother by His naughty activities, and she wanted to bind Him up. Mother Yaśodā brought some rope from the house and tried to tie up the child, but she could not tie a knot due to the shortness of the rope. She tied together many ropes, but when she finished still the rope was too short. After a while she felt very tired and began to perspire. At that time Kṛṣṇa agreed to be bound up by His mother. In other words, no one can bind Kṛṣṇa by any means other than love. He is bound only by obligation to His devotees, because of their ecstatic love for Him.