For Martial Classes, the Magic stat doesn't figure into battle related things, but consider it your "knowledge" of magic, as in how much your character knows about how it works and stuff like that, which might help you form a strategy against it. It will figure in more once we've gotten some enchanted loot, because special types of items will have effects that draw from the Magic stat. Other things might use it too, such as perhaps needing a certain knowledge of magic and a certain resistance to it in order to see through a magical illusion in a dungeon.