To what extent does the reader feel the presence of Arthur Miller in The Crucible?

The reader can feel the presence of the play's author, Arthur Miller, in the frequent expository passages that occur in the first act.  In fact, after the description of the setting, Miller begins to give us background on both Reverend Parris and the Puritans in general.  He even already begins to show how the story of the witch hunts in Salem hundreds of years ago remain relevant and, indeed, has parallels in modern America. 

Further, after the Putnams arrive, Miller provides background information about them, including information regarding Thomas Putnam's "vindictive nature" and the fact that he and his daughter are so instrumental in making accusations.  Such passages as these help us to understand who Miller blames for the tragedies that follow.  In addition, Miller interjects to describe John Proctor.  This introduction, especially, allows readers to understand the changes that Miller makes to the real-life people on whom characters are partially based, or at least for whom they are named.  Proctor, for instance, is in his mid-thirties in the play, but the real-life John Proctor was in his sixties.  Likewise, Miller's introduction of Francis and Rebecca Nurse portrays them as largely sympathetic figures, especially compared to the angry and vindictive Putnams. 

Similarly, Miller introduces Reverend Hale and Giles Corey, again, to help us understand who they are, what motivates them, and how guilty or guiltless they may prove to be, at least for Miller.  These interjections cease after the first act is over, but Miller has made his position known on those characters who require more than just their own words to make them truly known to us.