The camera does not like acting. The camera is only interested in filming behaviour. So you damn well learn your lines until you know them inside out, while standing on your head!
Semantics, or the study of meaning, remained undeveloped, while phonetics made rapid progress and even came to occupy the central place in the scientific study of language.
Theatre is simply what cannot be expressed by any other means; a complexity of words, movements, gestures that convey a vision of the world inexpressible in any other way.