Beyond the planetary systems in the material sky, there is another sky, which is known as paravyoma, or the spiritual sky, where there are spiritual planets. The inhabitants of those planets engage in varieties of loving service unto the Supreme Personality of Godhead, which include different rasas, or relationships, known as dāsya-rasa, sakhya-rasa, vātsalya-rasa, mādhurya-rasa and, above all, parakīya-rasa.
(Srimad Bhagavatam------4:20:35-36------purport).

Vātsalya-rati is described as follows in the Bhakti-rasāmṛta-sindhu (2.5.33):
guravo ye harer asya te pūjyā iti viśrutāḥ
anugraha-mayī teṣāṁ ratir vātsalyam ucyate
idaṁ lālana-bhavyāśīś cibuka-sparśanādi-kṛt
When a living entity is situated on the platform of vātsalya-rati, he thinks of the Supreme Personality of Godhead in His childhood feature. In this feature, the Lord has to be protected by the devotee, and at this time the devotee takes the position of being worshiped by the Supreme Personality of Godhead. These feelings of parental love are called vātsalya-rati. When the devotee is situated on this platform, he wants to maintain the Lord like a son, and he desires all good fortune for the Lord. He offers blessings to the Lord by touching His feet and head.
(Sri Caitanya Caritamrta------2:19:183-------purport).

One must go further and further into spiritual understanding. The first realization is impersonal Brahman, but one must go still further to realize Paramātmā and eventually the Supreme Personality of Godhead, who is worshiped by the transcendental feelings of a devotee in a relationship of śānta, dāsya, sakhya, vātsalya or mādhurya. Here the feelings of Prahlāda Mahārāja were in the mellow of vātsalya, filial love and affection. As a child cries when left by his mother, when Prahlāda Mahārāja felt that the Lord was away from him he began to cry (nadati). Again, a devotee like Prahlāda sometimes sees that the Lord is coming from a long distance to pacify him, like a mother responding to a child, saying, "My dear child, do not cry. I am coming." Then the devotee, without being ashamed due to his surroundings and circumstances, begins to dance, thinking, "Here is my Lord! My Lord is coming!" Thus the devotee, in full ecstasy, sometimes imitates the pastimes of the Lord, just as the cowherd boys used to imitate the behavior of the jungle animals. However, he does not actually become the Lord. Prahlāda Mahārāja achieved the spiritual ecstasies described herein by his advancement in spiritual understanding.
(Srimad Bhagavatam------7:4:40------purport).

Kṛṣṇa presented Himself as an innocent child to increase the transcendental ecstasy of maternal affection. As described in the śāstra, tāḍana-bhayān mithyoktirvātsalya-rasa-poṣikā. This means that sometimes a small child speaks lies. For example, he may have stolen something or eaten something and yet deny that he has done so. We ordinarily see this in the material world, but in relation to Kṛṣṇa it is different; such activities are meant to endow the devotee with transcendental ecstasy.
(Srimad Bhagavatam------10:8:35------purport).

In the spiritual world there are five kinds of relationships with the Supreme Lord—śānta, dāsya, sakhya, vātsalya and mādhurya. The perverted reflections of these rasas are found in the material world. Land, home, furniture and other inert material objects are related in śānta, or the neutral and silent sense, whereas servants work in the dāsya relationship. The reciprocation between friends is called sakhya, the affection of a parent for a child is known as vātsalya, and the affairs of conjugal love constitute mādhurya. These five relationships in the material world are distorted reflections of the original, pure sentiments, which should be understood and perfected in relationship with the Supreme Personality of Godhead under the guidance of a bona fide spiritual master. In the material world the perverted rasas bring frustration. If these rasas are reestablished with Lord Kṛṣṇa, the result is eternal, blissful life.
(Sri Caitanya Caritamrta------1:1:56-------purport).

After His appearance, Lord Kṛṣṇa thought that He had not distributed the transcendental personal dealings with His devotees in dāsya, sakhya, vātsalya and mādhurya. One may understand the science of the Supreme Personality of Godhead from the Vedic literatures and thus become a devotee of the Lord and worship Him within the regulative principles described in the scriptures, but one will not know in this way how Kṛṣṇa is served by the residents of Vrajabhūmi. One cannot understand the dealings of the Lord in Vṛndāvana simply by executing the ritualistic regulative principles mentioned in the scriptures. By following scriptural injunctions one may enhance his appreciation for the glories of the Lord, but there is no chance for one to enter into personal dealings with Him. Giving too much attention to understanding the exalted glories of the Lord reduces the chance of one's entering into personal loving affairs with the Lord. To teach the principles of such loving dealings, the Lord decided to appear as Lord Caitanya.
(Sri Caitanya Caritamrta------1:3:16-------purport).

Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura points out that in Vrajabhūmi there is the Yamunā River with its sandy banks. There are kadamba trees, cows, Kṛṣṇa's sticks with which He herds cows, and Kṛṣṇa's flute. All of these belong to śānta-rasa, the mellow of neutrality in devotional service. There are also the direct servants of Kṛṣṇa, such as Citraka, Patraka and Raktaka, and these are the embodiments of service in the mellow of servitude. There are also friends like Śrīdāmā and Sudāmā, who embody service in fraternity. Nanda Mahārāja and mother Yaśodā are the embodiments of parental love. Above all of these are Śrīmatī Rādhārāṇī and Her assistants, the gopīs Lalitā, Viśākhā and others, who embody conjugal love. In this way all five mellows—śānta, dāsya, sakhya, vātsalya and mādhurya—exist eternally in Vrajabhūmi. They are also compared, respectively, to copper, bell metal, silver, gold and touchstone, the basis of all metals. Śrīla Kavirāja Gosvāmī therefore refers to a mine eternally existing in Vṛndāvana, Vrajabhūmi.
(Sri Caitanya Caritamrta------2:8:294-------purport).

There are different types of devotees—those in śānta-rasa, dāsya-rasa, sakhya-rasa, vātsalya-rasa and mādhurya-rasa. Although all the rasas are on the transcendental platform, mādhurya-rasa is the supreme transcendental mellow. Consequently it is concluded that the worship of devotees engaged in the Lord's service in mādhurya-rasa is the supreme spiritual activity. Śrī Caitanya Mahāprabhu and His followers mainly worship Lord Kṛṣṇa in mādhurya-rasa. Other Vaiṣṇava ācāryas recommended worship up to vātsalya-rasa. Therefore Śrīla Rūpa Gosvāmī in his Vidagdha-mādhava (1.2) describes Śrī Caitanya Mahāprabhu's cult as supreme:
anarpita-carīṁ cirāt karuṇayāvatīrṇaḥ kalau
samarpayitum unnatojjvala-rasāṁ sva-bhakti-śriyam
Śrī Caitanya Mahāprabhu appeared in this Age of Kali to exhibit the superexcellence of mādhurya-rasa, a gift never previously bestowed by any ācārya or incarnation.
(Sri Caitanya Caritamrta------2:11:31-------purport).

In the fourth stage, called vātsalya-rati, the fraternal affection evinced in the preceding stage develops into paternal affection. At this time the living entity tries to be the parent of God. Instead of worshiping the Lord, the living entity, as a parent of the Supreme, becomes an object of worship for the Supreme Person. At this stage the Lord depends on the mercy of His pure devotee and puts Himself under the control of the devotee to be raised. The devotee in this stage attains the position wherein he can embrace the Supreme Lord and even kiss His head.
(Teachings of Lord Caitanya).

When one attains śānta-rasa, unflinching faith in Kṛṣṇa is established, and all material desires cease. These specific characteristics of śānta-rasa—unflinching faith in Kṛṣṇa and cessation of all desires which are not connected with Kṛṣṇa—are common to all other rasas as well, just as sound is generally present in all other elements (air, fire, water and earth) because it is produced from the sky. Similarly, these two characteristics of śānta-rasa are present in other transcendental relationships, such as dāsya (servitorship), sakhya (fraternity), vātsalya (paternal affection), and the madhura-rasa (conjugal love).
(Teachings of Lord Caitanya).

Rāgānuga-bhakti, or spontaneous devotional service, can be executed in the śānta-rasa when one aspires to be like Kṛṣṇa's cows or the stick or flute in the hand of Kṛṣṇa, or the flowers around Kṛṣṇa's neck. In the dāsya-rasa one follows in the footsteps of servants like Citraka, Patraka or Raktaka. In the friendly sakhya-rasa one can become a friend like Baladeva, Śrīdāmā or Sudāmā. In the vātsalya-rasa, characterized by parental affection, one can become like Nanda Mahārāja and Yaśodā, and in the mādhurya-rasa, characterized by conjugal love, one can become like Śrīmatī Rādhārāṇī or Her lady friends such as Lalitā and Her serving maids (mañjarīs) like Rūpa and Rati.
(Nectar of Instruction).