In "Young Goodman Brown" by Nathaniel Hawthorne, what specific sins does the devil promise the potential communicant he will learn to recognize? What deeper mysteries will he come to understand?
The devil promises that potential communicants will learn how women, eager to become widows, give "[their] husband[s] a drink at bedtime." In other words, these women poison their spouses in order to seize independence for themselves. Moreover, communicants will learn of "beardless youths" who have killed their fathers so that they can inherit their wealth early. Further, communicants will learn about "fair damsels" who have "dug little graves in the garden" and asked the devil himself to be the sole mourner at a baby's funeral. In other words, these young women are supposed to be maidens, and so, if they have sex and become pregnant, they kill the babies in order to preserve their appearance of virginity and innocence.
In addition, the communicants will come to understand that "the whole earth [is] one stain of guilt, one mighty blood spot." This is so because everyone is guilty of sin; there is no one, not even the most pious-seeming old man or woman, who has not committed some egregious sin against God. Furthermore, communicants will learn to
"penetrate, in every bosom, the deep mystery of sin, the fountain of all wicked arts, [...] which inexhaustibly supplies more evil impulses than human power -- than [the devil's] power, at its utmost! -- can make manifest in deeds."
They are promised the ability to tap into some hellishly sacred font of sin, to understand that sin is absolutely the nature of all things in the world.