He put the South on the map and the edge back in hegemony.
We hear you, reluctant Shmooper. You're wondering why on earth a labor organizer and Marxist theorist's writings are required reading for students of literature.
Here's why: Gramsci made the study of culture a must for leftists and rightists alike. Against hard-liners who only wanted to be shown the money—to go straight to what they thought made the world go round ($$), bypassing inessential things like language and literature in the process—Gramsci said, loudly and clearly: hold up.
Gramsci schooled both his Fascist opponents and his left-leaning fellow travelers in more ways than one. This guy made them all think again about everything from high art to popular culture, from "normative grammar" to "common sense." (Don't worry—we're gonna get on that.)
Gramsci showed that cultural forces are essential to the workings of power; they're not a mere afterthought or just some icing on the cake. Gramsci let everyone know that power needed culture—and this meant that in order to understand power, theorists had to spend time reckoning with the culture as well. They had to take lit, and crit, and opera, and school textbooks, and all kinds of other harmless-looking stuff like that seriously if they wanted to understand how power worked.
That's why generations of heavy-hitting theorists have followed Gramsci's lead. That's also why you've been led here, Shmoopers. Gramsci gave cultural theory a new lease on life by demonstrating just how powerful culture can be, for better and worse.