The major theme of The Scarlet Letter is shaming and social stigmatizing, both Hester's public humiliation and Dimmesdale's private shame and fear of exposure. Notably, their liaison is never spoken of, so the circumstances that lead to Hester's pregnancy, and how their affair was kept secret never become part of the plot.
Elmer Kennedy-Andrews remarks that Hawthorne in "The Custom-house" sets the context for his story and "tells us about 'romance', which is his preferred generic term to describe The Scarlet Letter, as his subtitle for the book – 'A Romance' – would indicate." In this introduction, Hawthorne describes a space between materialism and "dreaminess" that he calls "a neutral territory, somewhere between the real world and fairy-land, where the Actual and the Imaginary may meet, and each imbues itself with nature of the other". This combination of "dreaminess" and realism gave the author space to explore major themes.
The experience of Hester and Dimmesdale recalls the story of Adam and Eve because, in both cases, sin results in expulsion and suffering. But it also results in knowledge - specifically, in knowledge of what it means to be immoral. For Hester, the Scarlet Letter is a physical manifestation of her sin and reminder of her painful solitude. She contemplates casting it off to obtain her freedom from an oppressive society and a checkered past as well as the absence of God. Because the society excludes her, she considers the possibility that many of the traditions held up by the Puritan culture are untrue and are not designed to bring her happiness.
As for Dimmesdale, the "cheating minister", his sin gives him "sympathies so intimate with the sinful brotherhood of mankind, so that his chest vibrate[s] in unison with theirs." His eloquent and powerful sermons derive from this sense of empathy. The narrative of the Reverend Arthur Dimmesdale is quite in keeping with the oldest and most fully authorized principles in Christian thought. His "Fall" is a descent from apparent grace to his own damnation; he appears to begin in purity but he ends in corruption. The subtlety is that the minister's belief is his own cheating, convincing himself at every stage of his spiritual pilgrimage that he is saved.
The rose bush's beauty forms a striking contrast to all that surrounds it; as later the beautifully embroidered scarlet "A" will be held out in part as an invitation to find "some sweet moral blossom" in the ensuing, tragic tale and in part as an image that "the deep heart of nature" (perhaps God) may look more kindly on the errant Hester and her child than her Puritan neighbors do. Throughout the work, the nature images contrast with the stark darkness of the Puritans and their systems.
Chillingworth's misshapen body reflects (or symbolizes) the anger in his soul, which builds as the novel progresses, similar to the way Dimmesdale's illness reveals his inner turmoil. The outward man reflects the condition of the heart; an observation thought inspired by the deterioration of Edgar Allan Poe, whom Hawthorne "much admired".
Another theme is the extreme legalism of the Puritans and how Hester chooses not to conform to their rules and beliefs. Hester was rejected by the villagers even though she spent her life doing what she could to help the sick and the poor. Because of the social shunning, she spent her life mostly in solitude, and would not go to church.
As a result, she retreats into her own mind and her own thinking. Her thoughts begin to stretch and go beyond what would be considered by the Puritans as safe or even Christian. She still sees her sin, but begins to look on it differently than the villagers ever have. She begins to believe that a person's earthly sins do not necessarily condemn them. She even goes so far as to tell Dimmesdale that their sin has been paid for by their daily penance and that their sin will not keep them from getting to heaven, however, the Puritans believed that such a sin surely condemns.
But Hester had been alienated from the Puritan society, both in her physical life and spiritual life. When Dimmesdale dies, she knows she has to move on because she can no longer conform to the Puritans' strictness. Her thinking is free from religious bounds and she has established her own different moral standards and beliefs.