Secret sin is one of the themes most focused on in Nathaniel Hawthorne's The Scarlet Letter. Each of the three main characters, Hester, Dimmesdale, and Chillingworth, has his or her own secret sins. Hester's secret sin is not confessing the identity of Pearl's father. Likewise, Reverend Dimmesdale's secret sin is committing adultery with Hester. Committing a much darker sin, Roger Chillingworth, Hester's husband, is guilty of violating another human's heart and soul. All of these characters wish to confess their sins to lift the burden of guilt off of their shoulders, but only one of them is truly able to confess. Each Character has a secret sin that he or she wishes to confess and each of those sins affects the character that committed that sin as well as other characters in the story.
Hester's sin is highly influential in this story because it affects each of the characters involved. Her sin, which is not revealing her sexual partner, weighs heavily on her conscience and also leads to torment from other people who want to know the identity of Pearl's father. Because she feels the obligation to keep her sin hidden, for the purpose of protecting Dimmesdale, Hester does so. This silence, which is not wished for by Dimmesdale, causes Hester, as well as Dimmesdale, a great deal of inner guilt and pain. The silence causes Hester a great deal of corruption as well. At one point she even considered killing Pearl and then herself to rid them of their misery. Hester's sin weighs on Dimmesdale's conscience, so much so, that it causes Dimmesdale to become ill. For a much different reason, Hester's sin affects Chillingworth as well. Since Hester does not reveal the identity of her lover, Chillingworth makes it his life-long goal to discover that identity and to seek his revenge on that person. This will eventually cause Chillinworth to become spiritually and physically ill. .
Although Hester is protagonist, and her sin is very influential, Dimmesdale's sin is probably the most important sin in The Scarlet Letter because it started the whole story.