To answer this question I would focus on the character of Arthur Dimmesdale, which is the main focus of this chapter, and the way that he is presented as struggling as a result of the conflict between his public image and his private self. One of Hawthorne's themes that his fiction develops again and again is the hypocrisy of Puritan society, and the way that even the most noble and morally upright characters are shown to suffer from secret sins that they may or may not be able to reveal.
This chapter shows the impact of Dimmesdale's grief upon his teaching and preaching, and ironically his secret guilt makes him extremely popular and gives his sermons new relevance that his congregation can readily relate to. Note how it is described in this chapter:
But this very burden it was that gave him sympathies so intimate with the sinful brotherhood of mankind; so that his heart vibrated in unison with theirs, and received their pain into itself, and sent its own throb of pain through a thousand other hearts, in gushes of sad, persuasive eloquence.
Ironically, it is the very guilt that Dimmesdale is so ashamed of and which he feels he cannot be open about that makes him successful as a pastor. He can speak compellingly and authentically about sin because he himself is a sinner and understands the way that sin impacts a man's life by separating him from others and forcing him to lead a miserable existence. The themes of guilt and sin in the novel, and this chapter and its presentation of Dimmesdale is key to understanding the complex message that Hawthorne is trying to convey.