The overarching sin that the people Goodman Brown meets in the woods are guilty of is worshipping Satan. Goodman Brown finds them all attending or en route to attending a Black Mass.
Because many of these people, such as Goodye Cloyse, the minister, and Deacon Gookin, have posed as pious Christians, they are guilty of hypocrisy, which is pretending to be what you are not. Rather than living lives of goodness and sacrifice to others, full of love and charity, they have sold their souls to the devil in return for personal gain on earth. Faith, too, is a devil worshipper. Goodman Brown believed she was sexually pure and faithful to him, but she participates in a Walpurgis Night orgy.
It is unclear if what Goodman Brown witnessed really happened or was a dream. Whatever the case, all humans are mixes of good and evil, a fact Goodman Brown finds...
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