If you rub the brisket with the spice mixture and immediately place it in the oven, it’s just a rub. It will flavor the exterior of the meat, and the spices will penetrate a little way into the beef. But if you rub the seasonings into the brisket and let it sit overnight before roasting, this would be considered a brisket dry brine. The salt and other seasonings will have time to truly work their way into the center of the beef, giving you a more flavorful piece of meat.