Why are the books of prophecy categorized as "major" and "minor"? What makes one major and another minor? -- Dovie Bohnhoff
In Latin, the language of medieval scholarship and theology, major (maior) means greater, while minor means lesser. So the terms have only to do with their length, not necessarily their theological importance. (Although who would deny that Isaiah, the most quoted prophet in the NT and replete with references to the coming Messiah, is on the same level of importance with, say, Obadiah?)
Anyway, the major prophets are the longer books; minor ones, the shorter books. Easy as pie!