The refers to the person or people who will first see and evaluate your work.

the third answer is right : )

i hope this you with your work! : )

edwards uses the phrase "o who can express what the state of a soul in such circumstances is! " in order to illustrate that this type of suffering is unimaginable. the word "express" denoted that the state of a suffering soul is required to be described by any person, but it would not happen because no one can imagine how this suffering is felt.  

-show what might happen if the reader disobeys edwards is not correct because this is described trhough the text, not by the phrase used.

-describe what endless suffering looks and feels like is not correct because this description might be the porpuse of the excerpt provided, not the porpuse of using the phrase during the writting.

-prove that few people have survived limitless suffering is not correct because it is implied that the soul of a person is already suffering and doesn't have any way to escape.