As in so many of Hawthorne's works, there is an intentional ambiguity on the author's part in "Young Goodman Brown." And, it may be that this ambiguity is created so that the readers will become involved in an analysis themselves of what constitutes sin. One interpretation of the devil, for instance, is that he represents the darker side of Goodman Brown himself.  For, he resembles Goodman and he claims to know Goodman's grandfather.  In their dialogue, Goodman declares his virtue, while the old man laughs, suggesting the scoffing of a darker nature at the hypocritical efforts of piety. 

Within Puritanism there is the Calvanistic concept of Total Depravity.  That is, the heart, emotions, will, mind, and body are all afflicted with sin.  This concept is expostulated by the devil when he says,

By the sympathy of your human hearts for sin ye shall scent out all the places—whether in church, bedchamber, street, field, or forest—where crime has been committed, and shall exult to behold the whole earth one stain of guilt, one mighty blood spot. Far more than this. It shall be yours to penetrate, in every bosom, the deep mystery of sin, the fountain of all wicked arts, and which inexhaustibly supplies more evil impulses than human power—than my power at its utmost—can make manifest in deeds. And now, my children, look upon each other.”

Earlier Goodman Brown has stepped out of the woods in which he has hidden and approached the congregation "with whom he felt a loathful brotherhood by the sympathy of all that was wicked in his heart." Now, he is part of those to whom the devil addresses himself since he recognizes the "shape" of his own father in the devil.

Then, when Faith's pink ribbons fly into the air, the symbolism of these ribbons suggests her loss of innocence.  But, Goodman is not certain of the events that follow when he seems to awaken from a dream.  However, because he has lost his faith--having become "part of those to whom the devil addresses himself," it is a gloomy and distrustful Goodman Brown who emerges from the forest.  He has passed from naivete to the recognition of the depravity and evil of man's nature.