Aside from discussing the writer's work, Mr. Stoppard discusses aspects of the collaboration between the writer and the actor.
I emphasis to actors their need to hold the dialogue of every script sacred; every word in every sentence sacred -- to not paraphrase, add or substitute words regardless of how mediocre the actor thinks the dialogue is. The story is not about you. The execution of telling the story is about how what the writer has written resonates for you so that the character you create is the third party to your collaboration with the writer, and as I've mentioned earlier, the final collaborator is the audience, and not necessarily every member of the audience, as Mr. Stoppard comments here.
The actor limits himself and chokes his ability to create a unique human being when he tries to tailor the written sentences to himself.