Para-tattva, the embodiment of non-dual knowledge, is Himself rasa, transcendental mellow. Those who have had no experience of rasa-tattva cannot realize the Absolute Truth in the slightest. In Taittirīya Upaniṣad (2.7) it has been said:
raso vai saḥ, rasaṁ hyevāyaṁ labdhvānandī bhavati, ko hyevānyāt kaḥ prāṇyāt, yadeṣa ākāśa ānando na syāt, eṣa hyevānandayāti
Para-tattva Himself is rasa. On attaining that rasa, the jīva experiences true bliss (ānanda). If that undivided Reality were not the embodiment of ānanda in the form of rasa, then who could remain alive and who would endeavour to live? He alone gives pleasure to all.
Prior to Svayam Bhagavān Śrī Caitanya Mahāprabhu, different Vaiṣṇava ācāryas had established, preached and propagated bhakti-tattva. However, only Śrī Rūpa Gosvāmī, being empowered by Śrī Caitanya Mahāprabhu, further developed that bhakti-tattva into bhakti-rasa. He described this subject elaborately in his Bhakti-rasāmṛta-sindhu and Ujjvala-nīlamaṇi. He explained that the bhakti-lātā-bīja in the form of kṛṣṇa-sevā-vāsanā, the inclination to serve Kṛṣṇa, develops sequentially from śraddhā to niṣṭhā, ruci and āsakti. When it is transformed into rati, it is called sthāyībhāva. When the four bhāvas, namely, vibhāva, anubhāva, sāttvika and vyābhicārī, join in a combined form in this sthāyībhāva, then rati in the form of sthāyībhāva is transformed into a relishable and supremely astonishing condition called bhakti-rasa.
The movement governing both mundane rasa and pure spiritual rasa are the same. When the application of the sthāyībhāva is in relation to Bhagavān, there is pure spiritual bhakti-rasa, whereas when sthāyībhāva is in relation to material sense enjoyment, there is insignificant, mundane rasa. Where the sthāyībhāva is applied in relation to non-differentiated knowledge there is nirviśeṣa-brahma-rasa, and where it pertains to yoga, there is paramātmā-rasa. Before śraddhā develops into rati, the endeavour for rasa from the combination of the constituent bhāvas such as vibhāva, results in incomplete, fragmented rasa. Mundane rasa is thoroughly rejectable and insignificant. Only spiritual rasa is being considered herein.
Rati, in the form of sthāyībhāva, is the foundation of rasa. Rasa comes from the union of its four constituent ingredients, namely, vibhāva, anubhāva, sāttvika and vyabhicārī. Vibhāva is of two types: ālambana and uddīpana. Ālambana is also divided into two: āśraya and viṣaya. The possessor of sthāyībhāva is called the āśraya (abode) of rasa, and the one towards whom sthāyībhāva is directed is the viṣaya (object) of rasa. In transcendental rasa, Śrī Kṛṣṇa is the only object (viṣaya) of rasa and the worshiper is the abode (āśraya) of rasa. The qualities of the worshipful object and objects in relation to Him are called uddīpana. Dancing, singing, yawning, hiccupping and so on are expressions of the bhāva within the heart, and are therefore called anubhāvas. Bodily transformations such as becoming stunned, perspiration and horripilation are called sāttvika-bhāvas because they are manifested from pure spiritual existence, or sattva. There are thirty-three types of vyabhicārī-bhāvas, such as self-disparagement, despondency and humility. These bhāvas move in the direction of the ocean of the sthāyībhāva and increase it. Therefore they are called vyabhicārī.
Rasa is of two types, namely, primary (mukhya) and secondary (gauṇa). The five mukhya-rasas are śānta (passive adoration), dāsya (servitude), sakhya (friendship), vātsalya (parental love) and madhurya (amorous love). The seven secondary rasas are hāsya (comedy), adbhuta (astonishment), raudra (anger), vīra (chivalry), karuṇa (pathos), bhayānaka (horror) and vībhatsa (disgust).
Śrīla Rūpa Gosvāmī has given a fresh and comprehensive definition of bhakti:
The cultivation of activities which are meant exclusively for the pleasure of Śrī Kṛṣṇa, or in other words, the uninterrupted flow of service to Śrī Kṛṣṇa, performed through all endeavours of the body, mind and speech, and through the expressions of various spiritual sentiments (bhāvas), which is not covered by jñāna (knowledge aimed at impersonal liberation) and karma (reward-seeking activity), and which is devoid of all desires other than the aspiration to bring happiness to Śrī Kṛṣṇa, is called uttama-bhakti, pure devotional service.
By performing sādhana for this type of bhakti, rati is awakened. When rati becomes more condensed it is called prema. As that prema matures and thickens, it is known successively as sneha, māna, praṇaya, rāga, anurāga, bhāva and mahābhāva. Kṛṣṇa-rati is also of five types, arising from five divisions of devotees: śānta, dāsya, sakhya, vātsalya and madhura. Among these, madhura-rati is the best.
Kṛṣṇa-prema is also of two types – aiśvarya-miśrita and kevala, or pure, prema. The prema by which one considers Kṛṣṇa to be the Supreme Godhead endowed with six opulences and oneself to be destitute, low and insignificant is called aiśvarya-miśrita, or mixed with knowledge of Kṛṣṇa’s opulences. The prema that we see in the material world is mainly this mixed prema, which does not control Bhagavān. Kevala, or pure, prema is that pure affection through which one considers Kṛṣṇa to be one’s son, friend or sweetheart, exactly as in an intimate worldly relationship.
Kṛṣṇa is only controlled by this kevala-prema. Yaśodā-maiyā scolds Kṛṣṇa and binds Him by her pure parental affection. In their pure sakhya-bhāva, Kṛṣṇa’s friends climb on His shoulders. The charming gopīs of Vraja consider Kṛṣṇa their most dear one, and when they rebuke Him, their words of reproach are even more pleasing to Śrī Kṛṣṇa than the Vedic hymns sung by Brahmā. If Vrajendra-nandana Śyāmasundara had not descended to this world, then the subjects of these three elevated levels of rasa, namely, sakhya, vātsalya and madhura, would not be found and the material world would remain deprived of these elevated sentiments. Specifically, if Śrī Kṛṣṇa had not mercifully manifested His cowherd boy pastimes, which madden the world with love, then no one would even be able to realize that Parameśvara is the object of madhura-rasa.
Among Kṛṣṇa’s pastimes, vraja-līlā is the best of all, because in this very pastime the highest benefit of all the jīvas is obtained in regard to rasa. Logicians and worldly moralists cannot touch the glories of kṛṣṇa-līlā. Vraja-līlā is composed entirely of rasa, and those who can carry this līlā in their hearts are very fortunate. Only those fortunate devotees who have tasted the sweetness of vraja-līlā can know its sweetness. It is impossible to enter this subject by logic, morality, knowledge, yoga, religion or irreligion.
Śrī Kṛṣṇa, the embodiment of rasa, is the Supreme Reality, or para-brahma. At the same time, He is supremely rasika, expert in relishing the mellows of love. Therefore, although He is one, in order to taste rasa, He is eternally situated in four natural forms by the influence of His own inconceivable potency. Śrīla Jīva Gosvāmī has described these four natural forms in his Bhagavat-sandarbha (14): “ekam eva taṁ paramaṁ tattvaṁ svābhāvikācintya-śaktyā sarvadaiva svarūpa-tad-rūpa-vaibhava-jīva-pradhāna-rūpeṇa caturddhāvatiṣṭhate, sūryāntara-maṇḍala-stha-teja iva, maṇḍala-tad-bahirgata-raśmi-tat-praticchavi-raśmyādi-rūpeṇa – Parama-tattva is one. He is equipped with His inconceivable natural potency. With the assistance of that potency, He is eternally manifest in four forms: His original form (svarūpa); His personal splendour, which includes His abode, eternal associates and expansions such as Lord Nārāyaṇa (tad-rūpa-vaibhava); the living entities (jīvas); and the unmanifest state of the three modes of material nature (pradhāna). There are some simple examples which partially illustrate this point. The four features may be compared to the effulgence situated in the interior of the sun planet, the sun globe, the rays of the sun emanating out from the globe, and a remote reflection of the sun, respectively.”
In the scriptures that describe the essential purports of the Vedas such as Śrīmad-Bhāgavatam, the spiritual authorities (mahājanas) have researched the pure rasa within Kṛṣṇa. Great sages such as the Catuḥsana (the four Kumāras) headed by Sanaka Kumāra, as well as Śiva, Vyāsa and Nārada have described the rasa within Kṛṣṇa’s supernatural pastimes in their own respective scriptures, having realized it in trance. But only Śrī Caitanya Mahāprabhu has manifested this nectarean śrī kṛṣṇa-rasa on the Earth. Before Him and until today, no one has been able to do this. Therefore, in Śrī Caitanya-candrāmṛta (130), Śrī Prabodhānanda Sarasvatī has stated quite appropriately:
prema-nāmādbhutārthaḥ śravaṇa-patha-gataḥ kasya nāmnāṁ mahimnaḥ
ko vettā kasya vṛndāvana-vipina-mahā-mādhurīṣu praveśaḥ
ko vā jānāti rādhāṁ parama-rasa-camatkāra-mādhurya-sīmā-
mekaś caitanya-candraḥ parama-karuṇayā sarvam āviścakāra
O brother, who had even heard of the name of the ultimate goal of life, called prema?
Who knew the glories of śrī harināma? Who had entered into the wonderful sweetness of Śrī Vṛndāvana? And indeed, who knew Śrīmatī Rādhikā, the parā-śakti (transcendental potency) as the pinnacle of the supremely astonishing mādhurya-rasa? Only the most merciful Śrī Caitanya-candra has uncovered all these truths out of compassion for the jīvas.