There is a remarkable nimbleness of style, a balancing act of tone, in Voltaire, which is hard to bring off on stage. When you speak the words out loud, the effect is very different from when you read them. So one needs to do something new with a stage performance, not simply 'tell the story'.
What we're seeking to do is internalize perception. Perception is very much involved with the senses and the mental processes and the emotional processes.