In Chapter XX, "The Minister in a Maze," the Reverend Dimmesdale learns that the ship for England upon which he and Hester plan to depart will not leave for four days. "That is most fortunate!" he remarks, for he will be able to deliver his Election Day sermon; this occasion, he feels, will be suitable for him to terminate his career.
'At least, they shall say of me,' thought this exemplary man, 'that I leave no public duty unperformed, nor ill performed!'
Hawthorne, as narrator comments,
Sad, indeed, that as introspection so profound and acute as this poor minister's should be so miserable deceived! We have had,...worse things to tell of him; but none, we apprehend, so pitiable weak; no evidence, at once so slight and irrefragable, of a subtle disease, that had long since begun to eat into the real substance of his character.
Poor Arthur Dimmesdale has been deceiving the residents of his community for so long that he has begun to deceive himself. This sad delusion is the "subtle disease" of which Hawthorne writes. Guilt leads to hypocrisy which, in turn, leads to self-deception. Hawthorne profoundly remarks,
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.
In the final chapter, XXIV, Hawthorne cautions against this condition in his statement of theme:
Among many morals which press upon us from the poor minister's miserable experience, we put only this into a sentence: 'Be true! Be true! Be true! Show freely to the world, if not your worst, yet some trait whereby the worst may be inferred!'