Kṛṣṇa wants only loving service and nothing more. Kṛṣṇa accepts even a little flower from His pure devotee. He does not want any kind of offering from a nondevotee. He is not in need of anything from anyone, because He is self-sufficient, and yet He accepts the offering of His devotee in an exchange of love and affection. To develop Kṛṣṇa consciousness is the highest perfection of life.
(Bhagavad-Gita------9:26------purport).

Rādhā and Kṛṣṇa are one, and when Kṛṣṇa desires to enjoy pleasure, He manifests Himself as Rādhārāṇī. The spiritual exchange of love between Rādhā and Kṛṣṇa is the actual display of the internal pleasure potency of Kṛṣṇa. Although we speak of "when" Kṛṣṇa desires, just when He did desire we cannot say. We only speak in this way because in conditional life we take it that everything has a beginning; however, in the absolute or spiritual life there is neither beginning nor end. Yet in order to understand that Rādhā and Kṛṣṇa are one and that They also become divided, the question "When?" automatically comes to mind. When Kṛṣṇa desired to enjoy His pleasure potency, He manifested Himself in the separate form of Rādhārāṇī, and when He wanted to understand Himself through the agency of Rādhā, He united with Rādhārāṇī, and that unification is called Lord Caitanya.
(Teachings of Lord Caitanya).

This brings up the question of who Rādhārāṇī is and what Rādhā-Kṛṣṇa is. Actually Rādhā-Kṛṣṇa is the exchange of love. This is not ordinary love; Kṛṣṇa has immense potencies, of which three are principal: internal, external and marginal. In the internal potency there are three divisions: saṁvit, hlādinī and sandhinī. The hlādinī potency is the pleasure potency. All living entities have this pleasure-seeking potency, for all beings are trying to have pleasure. This is the very nature of the living entity. At present we are trying to enjoy our pleasure potency by means of the body in this material condition. By bodily contact we are attempting to derive pleasure from material sense objects. We should not think, however, that Kṛṣṇa, who is always spiritual, tries to seek pleasure on this material plane like us. Kṛṣṇa describes the material universe as a nonpermanent place full of miseries. Why, then, would He seek pleasure in the material form? He is the Supersoul, the supreme spirit, and His pleasure is beyond the material conception.
(Teachings of Lord Caitanya).

The particular loving mood or attitude relished in the exchange of love with the Supreme Personality of Godhead is called rasa, or mellow. The different types of rasa, when combined together, help one to taste the mellow of devotional service in the highest degree of transcendental ecstasy. Such a position, although entirely transcendental to our experience, will be explained in this section as far as possible, following in the footsteps of Śrīla Rūpa Gosvāmī.
(Nectar of devotion).

The Lord says that His nature is eternal, blissful and full of knowledge, and the living entities are part and parcel of the Supreme, as gold particles are part of a gold mine. Thus the living entity, in his spiritual position, is as good as gold, as good as Kṛṣṇa in quality. The difference of individuality continues, otherwise there would be no question of bhakti-yoga. Bhakti-yoga means that the Lord is there, the devotee is there and the activity of exchange of love between the Lord and the devotee is there. Therefore the individuality of two persons is present in the Supreme Personality of Godhead and the individual person, otherwise there would be no meaning to bhakti-yoga. If one is not situated in the same transcendental position with the Lord, one cannot serve the Supreme Lord. To be a personal assistant to a king, one must acquire the qualifications. Thus the qualification is to become Brahman, or freed from all material contamination.
(Bhagavad-Gita------14:26------purport).

Kuntī was conscious of the exalted position of Kṛṣṇa, whereas Yaśodā was not. Therefore Yaśodā's position was more exalted than Kuntī's. Mother Yaśodā got the Lord as her child, and the Lord made her forget altogether that her child was the Lord Himself. If mother Yaśodā had been conscious of the exalted position of the Lord, she would certainly have hesitated to punish the Lord. But she was made to forget this situation because the Lord wanted to make a complete gesture of childishness before the affectionate Yaśodā. Thisexchange of love between the mother and the son was performed in a natural way, and Kuntī, remembering the scene, was bewildered, and she could do nothing but praise the transcendental filial love. Indirectly mother Yaśodā is praised for her unique position of love, for she could control even the all-powerful Lord as her beloved child.
(Srimad Bhagavatam------1:8:31------purport).

Śrīla Viśvanātha Cakravartī Ṭhākura, one of the great ācāryas in the modern age, explains that anubhāva, or the glory of the Lord, is first appreciated by the devotee in ecstasy manifesting the symptoms of perspiring, trembling, weeping, bodily eruptions, etc., which are further enhanced by steady understanding of the glories of the Lord. Such different understandings of bhāvas are exchanged between Yaśodā and the Lord (binding the Lord by ropes) and in the chariot driving by the Lord in the exchange of love with Arjuna. These glories of the Lord are exhibited in His being subordinated before His devotees, and that is another feature of the glories of the Lord. Śukadeva Gosvāmī and the Kumāras, although situated in the transcendental position, became converted by another feature of bhāva and turned into pure devotees of the Lord.
(Srimad Bhagavatam------1:9:19------purport).

The Lord is situated as Himself, Lord Kṛṣṇa, the Supreme Personality of Godhead, and He is accompanied by His expansions like Lord Rāma, Baladeva, Saṅkarṣaṇa, Nārāyaṇa, Mahā-Viṣṇu and so forth. The devotees worship all these forms according to their liking, and the Lord, out of His affection, presents Himself as arcā-vigraha. He sometimes presents Himself personally before the devotee out of reciprocation or affection. A devotee is always fully surrendered to the loving service of the Lord, and the Lord is visible to the devotee according to the devotee's desires. He may be present in the form of Lord Rāma, Lord Kṛṣṇa, Lord Nṛsiṁhadeva and so on. Such is the exchange of love between the Lord and His devotees.
(Srimad Bhagavatam------5:7:9------purport).

Nanda Mahārāja was surprised that Yaśodā, Kṛṣṇa's mother, could have bound her beloved child in such a way. Kṛṣṇa was exchanging love with her. How then could she have been so cruel as to bind Him to the wooden mortar? Nanda Mahārāja understood this exchange of love, and therefore he smiled and released Kṛṣṇa. In other words, as Kṛṣṇa, the Supreme Personality of Godhead, binds a living entity in fruitive activities, He binds mother Yaśodā and Nanda Mahārāja in parental affection. This is His pastime.
(Srimad Bhagavatam------10:11:6------purport).

From this incident one should learn that for anything offered to Kṛṣṇa with love and affection, Kṛṣṇa can reciprocate many millions of times over, both materially and spiritually. The basic principle involved is an exchange of love. Therefore Kṛṣṇa teaches in Bhagavad-gītā (9.27):
yat karoṣi yad aśnāsi
yaj juhoṣi dadāsi yat
yat tapasyasi kaunteya
tat kuruṣva mad-arpaṇam
"O son of Kuntī, all that you do, all that you eat, all that you offer and give away, as well as all austerities that you may perform, should be done as an offering unto Me." With love and affection, one should try to give something to Kṛṣṇa from one's source of income. Then one's life will be successful.
(Srimad Bhagavatam------10:11:11------purport).