The Scarlet Letter(1850), The Power and the Glory(1940), and A Month of Sundays(1975) have some similarities in their protagonists and themes. Arhur Dimmesdale, Tom Marshfield and the whisky-priest are Protestant ministers and a Catholic priest, respectively. Two of them beget illegitimate daughters, Pearl and Brigitta, and Marshfield commits several adulteries. Their sins are greater than those of the common people. Is it possible that their sins are forgiven? John Updike published Roger`s Version(1986) and S(1988) successively after his A Month of Sundcays and these three novels are called the Scarlet Letter Trilogy: in which Roger Lambert parodies Roger Chillingworth, Tom Marshfield, Artlmr Dimmesdale, and Sarah Hester Prynne. It may be unreasonable to compare The Power and the Glory with The Scarlet Letter, but Dimmesdale and the whisky-priest have much in common in that they become humble, penitential and gain courage after recognizing their sins. In A Month of Sundays we meet Professor Chillingworth, Marshifield`s father-in-law and Ms Prynne, owner of the motel in the desert, which remind us that it is a parody of The Scarlet Letter, though there are many dissimilarities in the views on sex, religion and the way of communication. Dimmesdale becomes a misanthrope, the whisky-priest suffers from knowing that people hide him even though they are held in hostage, and Marshfield wants to emphasis through the theme of adultery that flesh should not be neglected, for soul and flesh are one. But they are given salvation after seven years of torment, several months of fugitive life, and a month of searching for reconciliation in the desert. As reviewed in the above, this paper is organized from the viewpoint of comparative literature horizontally and vertically, that is, the comparison of their themes and the relationship of their influence.