The oldest description of rasa as aesthetic category is found in the Nāṭyaśāstra, a treatise on the theatre art dated to the 2nd cent. BCE – 2nd cent. CE. The vast available Western scholarly literature on the topic always highlighted the aesthetic essence of rasa, whether it was likened to European aesthetic categories or recognised as an original achievement of the Oriental wisdom. Without shrugging off this latter view, I would like to stress that the ancient Indian concept of rasa contains numerous aspects which cannot be explained with purely aesthetic ideas. In itself, the word rasa is highly polysemical. It occurs as early as the Vedas, where it stands for the élan vital or juice of a plant, for potions and liquids in general, and milk and water in particular. A magic potion, not unlike an elixir or nectar, was also known as rasa (and was equivalent to amṛta). Last but not least, the word designated the pivotal and best part of a thing; the quintessence or essence of a phenomenon; taste, mentality, or an emotional state and even the religious feeling.
Of the many meanings of the word rasa, the traditional theoretical evaluation of the theatre selected only one – taste. Indeed, the understanding of the word rasa as taste also emerged in the Vedic period but had a rather specific connotation. According to the R̥gvedic hymn IX.113.3, the initial semantics of rasa as taste were related to the soma cult and meant not just any taste but the unique taste of soma as a real-life potion. The crucial ritual aspect of soma was related to the specific hallucinating intoxication into which it had the power to put gods and mortals (priests drank the soma potion in particular rites). Soma drinking belonged to esoteric rites in which the human body, like a vessel, was to be filled with a divine potion. The magic trance caused by soma elevated humans above their nature. Ecstasy born of it gave unique, superhuman experiences and made humans participants of the divine world.
It can be substantiated that the early ritual drama had for supreme goal the acquisition of a specific psycho-physical state by all adepts without exception, similar to the ecstatic experience of soma. The religious ecstasy close to the mystical feeling of communication with God (also enacted in the mystery play before the pious audience) came as an analogy of the hallucinogenic effect of soma, in its essence, quintessence and taste – to put it into one word: rasa.
The rasa concept as it figures in the Nāṭyaśāstra cannot be described as an aesthetic theory in the proper sense of the term. In the treatise rasa still bears a large cluster of meanings from the earlier stages of the evolution, when it was regarded not as an aesthetic, properly artistic notion from the world of the arts, but a phenomenon from another reality, sacral and defying expression. As I see it, three stages can be singled out in the evolution of the concept of rasa: first, its emergence as a symbolic expression of a ritualistic content; second, close in time to the Nāṭyaśāstra, when rasa evolved into a theoretical term and acquired a specific aesthetic content, which gradually ousted its sacral essence; and the third, when the aesthetic aspect became dominant, while the transcendental (alaukika) element of rasa was singled out and emphasized in the later philosophical and mystical tradition (first of all, in the concept of bhakti–rasa in the Gauḍīya Vaiṣṇavism and interpretation of it by Rūpa Gosvāmī). In my view, the sacral aspects and original ritualistic context were the reason for the outstanding popularity, broad dissemination and long-lasting tradition of the notion of rasa.