No doubt the theme of Rules and Order is a big deal in this myth. For strict King Pentheus, it's everything. The King of Thebes does all he can to keep his city orderly in the face Dionysus' chaotic influence. Unfortunately for Pentheus, he fails miserably, and Dionysus' wild Bacchanals become a fixture in Theban and Greek life for thousands of years. You could interpret the myth as a lesson of what happens when laws become too strict. If people aren't allowed to ever blow off some steam, eventually they're bound to explode.
Dionysus brings a special kind of madness everywhere he goes. It's not just the kind that gets you locked you up in a padded room. (Well it might, but that's not the point.) Dionysus' ritualistic Bacchanals are designed to take his followers into a frenzied state that transports them beyond the normal human world. When the Maenads reach the height of holy madness they become one with him and are capable of awful feats of strength and even magic of a kind. Though it may be horrifying to the law enforcing Pentheus, Dionysus sees his form of madness as a holy rite.