Simplify the following text for a Grade 11 native English-speaking person.
Original: Alexander M. Witherspoon , professor of English at Yale University , writes in a prefatory essay : Part II , which appeared in 1684 , is much more than a mere sequel to or repetition of the earlier volume .
Simplified: Expert critics think the second part is important , and brings in more ideas : `` Part II , which appeared in 1684 , is much more than a mere sequel to or repetition of the earlier volume .