An interesting question. It actually suggest very little, largely because it tells the reader many things about his mind very directly. (There's not much left to suggest.) The story tells readers that Goodman Brown is confident (when he feels justified), but then that he is quickly frightened. This blurs his thoughts. When he resumes his walk, we seem acting on habit. We seem him easily amazed, and easily led. All of these are qualities of mind. The story suggests that in heading into the woods at night, he is abandoning faith as he is leaving Faith (his wife) behind. The story suggests that he was overconfident, and that he is vulnerable as a result.