After the minister's clandestine meeting with Hester in the forest, Hester has convinced him that they must leave the colony and return to England where they can live together as a family. Arthur Dimmesdale departs, looking backward, uncertain of what he has truly experienced. With the quandary of public hypocrisy and private suffering seemingly solved now, Dimmesdale's mind is free to consider other possibilities, and, like a child released from rules, his spirit feels a sense of release. He considers that he yet has time to give the Election Sermon, deceiving himself that the townspeople will at least say he performed his duties to the end. Having held his sin within his heart so long, Dimmesdale has become delusional. Of this Hawthorne significantly writes,
No man, for any considerable period, can wear one face to himself, and another to the multitude, without finally getting bewildered as to which may be the true.
A transformation, however, does come over the spirit of Dimmesdale in his sense of release from his secret sin, as he feels that he has "flung down" his sin like "a cast-off garment." Describing this sense of release in Dimmesdale, as "a revolution in the sphere of thought and feeling," Hawthorne portrays Dimmesdale as incited to commit "wild, wicked things" as an outlet to having held so long his secret guilt. Like Peter, who denies his Lord three times, Dimmesdale commits three acts of wickedness. Yet, these great temptations and his conversation with Mistress Gibbins cause the minister to return to his thoughts that he is a powerless victim of fate and must bear his cross of guilt and sin:
Tempted by a dream of happiness, he had yielded himself, with deliberate choice, as he had never done before, to what he knew was deadly sin.
Realizing the great evil of his hypocrisy in concealing his sin for so long, Dimmesdale pulls back from his feelings of release in the forest with Hester; and, as he feels fate directing him more,
...Another man had returned out of the forest...with a knowledge of hidden mysteries which the simplicity of the former never could have reached. A bitter kind of knowledge that!
When he enters his house, Chillingworth greets him, but realizes that the minister no longer trusts him. Speaking of his forthcoming sermon, Chillingworth suggests that he give the minister medication, but Dimmesdale, sensing a looming fate that he must be punished for his sin, refuses him and, instead, speaks of going to "another world."
To preface this answer, it is important to remember that Hawthorne wrote this novel as an allegory. An allegory is defined as a literary work with two or more levels of meaning, one literal level and one on a symbolic level. In Chapter 20, Dimmesdale is confronted with the reality of his sin. He is a product of the Puritan Code that his passions could not outweigh. Puritans so seriously regarded adultery, prohibited by the 7th Commandment, that it was punishable by death. Dimmesdale, at this point, faces his demons. As the pastor of the colony and the father of Pearl, he is torn by a guilty conscience but is too much of a coward to stand by Hester and to announce his indiscretion. After the confrontation with the eldest female member of his church and the meeting with his deacon, he made his decision. Thus, he went back to his room and tried to write his sermon for the congregation, which he could not complete after he worked on throughout the night.