In order to answer this question fully, consider the long list of psychological and moral themes which run through this story. At its core The Scarlet Letter is about ostracism, judgment, hypocrisy, introspection, acceptance, forgiveness, and revolution. Humans find themselves facing all of these issues at one time or another, throughout our lives.
The Scarlet Letter is a classic because of how often its themes have been repeated in history. For every person (famous or not) who has done something against the acceptable "moral code," been publically shamed as a result, but ultimately did something revolutionary for a society or a culture, there is a comparison back to Hawthorne's most famous text.
I encourage you, a high school student, to consider how the story is personally relevent to you. Which character(s) have you ever identified with, personally? Which character(s) could you compare to people you know or circumstances which you've observed? Let this story resonate with you now, because certainly it will continue to do so throughout your life in different ways.