In terms of Hawthorne's theme contrasting "hidden sin versus revealed sin", how has Dimmesdale changed in The Scarlet Letter?
This theme is most evident in chapter 20 of the novel. The transformation begins after Hester and Dimmesdale had a secret meeting in the forest, and Hester convinces Dimmesdale that they need to leave behind the settlement and move back to England. At this point Hester is almost sure that Dimmesdale finally sees her point, and he assents. However, it is clear to the reader that he is dazed and confused. Part of it is because Hester has him realize that his role as a pastor is quite hypocritical. She is not judgmental about it, but she does point out that he is just not the image that he works so hard to keep.
"At least, they shall say of me," thought this exemplary man, "that I leave no public duty unperformed or ill-performed!" Sad, indeed, that an introspection so profound and acute as this poor minister's should be so miserably deceived!
Dimmesdale is, therefore free. He is free from his guilt of having sinned against Hester, because the latter has openly forgiven him. He is free from his committment as a priest because he now has a way out of the settlement. However, with freedom there is the danger of confusing becoming liberated with becoming a libertine. Unfortunately, Dimmesdale was too much a spoiled child of the people not to consider the latter alternative.
Hawthorne writes of Dimmesdale's sudden awakening quite symbolically. Just like the Bible uses the motif of "threes", Dimmesdale also does three particularly bad things. Twice he is mean and rude to a deacon and to a member of his church. Then, he wants to teach bad things to kids that are playing near the church. He wonder if this liberation has made him mad or if, instead, it had removed his soul away and given it to the devil.
Am I mad? or am I given over utterly to the fiend? Did I make a contract with him in the forest, and sign it with my blood? And does he now summon me to its fulfilment, by suggesting the performance of every wickedness which his most foul imagination can conceive?
Just in time, enters Mistress Hibbins, who basically tells him that she knows that he has been in the forest, and that he has been up to no good. This frightens Dimmesdale, who wonders if he has actually sold his soul. This shows the ambiguity and weakness of Dimmesdale's character.
As a result of this, Dimmesdale no longer dreams of a new life with Hester. He starts to shift again, as if he has again become liberated in a different manner and he starts speaking of leaving to "another world". He has come out of the forest knowing good and bad. His hidden sin made him an emanciated, shy and quiet enigma. His revealed sin made him wild with desire of being a libertine. He has perhaps finally met both sides, heaven and hell. It is now time to move on. And, again, he will move on without considering Hester nor Pearl.
Yes, to another world," replied the minister with pious resignation. "Heaven grant it be a better one; for, in good sooth, I hardly think to tarry with my flock through the flitting seasons of another year! But touching your medicine, kind sir, in my present frame of body I need it not.