The Iranian and Indo-Aryan branches separated quite early.
It is the Indo-Aryan branch that moved into eastern Iran and the south into the Indian subcontinent in the first half of the 2nd millennium BCE.
It is the primary liturgical language of Hinduism and the predominant language of most works of Hindu philosophy as well as some of the principal texts of Buddhism and Jainism.
Sanskrit, in its variants and numerous dialects, was the lingua franca of ancient and medieval India.
According to Biderman, the perfection contextually being referred to in the etymological origins of the word is its tonal--rather than semantic--qualities.