"Young Goodman Brown" is often read as an allegory of the biblical fall of man. In the Bible, Adam and Eve are living a blissful life in the Garden of Eden when a serpent comes and tempts them to eat from the tree of knowledge—something God has explicitly forbidden. When they eat the tree's fruit, the results are catastrophic: they are expelled from Eden and prevented from becoming immortal, and they've introduced sin to humankind, corrupting every human's nature from that moment forward.
In "Young Goodman Brown," Goodman Brown represents an everyman—a typical Puritan man of the time who is both pious and secretly curious about sin. His wife, Faith, represents faith, both in God and in humankind's goodness. When Goodman Brown chooses to leave Faith and venture into the forest, he meets a stranger (literally the devil) with a serpent staff. The serpent evokes the serpent in the Garden of Eden, and, fittingly, it's this man with the serpent staff who tempts Goodman Brown deeper into the forest, a journey that is akin to eating from the tree of knowledge.
Goodman Brown initially believes that he'll be able to indulge his curiosity about sin for just one night and then return unchanged to his happy life in Salem. But, just like Adam and Eve, Goodman Brown experiences a fall that expels him from the happy life he has known (allegorically, the Garden of Eden). In the forest, Goodman Brown believes that he sees Salem's virtuous elite consorting with the devil, which shakes his faith in the possibility of goodness. But what wounds him most deeply is seeing Faith in the forest, too. He believed that she was the embodiment of virtue and innocence, and her proximity to the devil turns Goodman Brown bitter and cynical for the rest of his life. In shattering his idealized notion of Faith, Goodman Brown literally loses his faith and his innocence. This is his allegorical expulsion from Eden, condemning him to misery for the rest of his life.
