All the best performers bring to their role something more, something different than what the author put on paper. That's what makes theatre live. That's why it persists.
I'm interested in the theater because I'm interested in communication with audiences. Otherwise I would be in concert music.
Musicals are, by nature, theatrical, meaning poetic, meaning having to move the audience's imagination and create a suspension of disbelief, by which I mean there's no fourth wall.
In the Rodgers and Hammerstein generation, popular hits came out of shows and movies.