Rasa, literally "juice" or "essence," is the ancient South Asian theory of aesthetic emotion: the distilled feeling a work of art produces in a receptive listener. Classical thought names a set of rasas — among them shringara (love), karuna (pathos), shanta (peace), bhakti (devotion) and vira (heroism) — and the goal of a raag performance is to evoke its particular rasa.
This is why mood is inseparable from raag. Darbari aims at a grave, majestic seriousness; Yaman at a romantic serenity; Bhairvi at tender devotion. The choices of notes, ornaments and performance time all serve the rasa.
Rasa connects music to the wider arts — the same theory governs classical poetry, dance and drama — and it is the deepest answer to why this music moves people: not display for its own sake, but the careful cultivation of feeling.