Northrop Frye was the quiet critic in the corner, away from the crowd, holding tight to powerful ideas that would change the way people thought about literature. Never one to brag or command attention, Frye spent his entire professional life teaching at the University of Toronto, where he proposed the idea that all books are based on timeless myths. No new-fangled ideas here.
Frye definitely wasn't a mainstream Structuralist. Like the Structuralists, he didn't believe that any literary ideas could ever be new, but unlike the Structuralists, he concocted his own categories (with charts and everything) that allowed him to categorize literature according to such categories as tragic, comic, and thematic.
Not afraid to drill deep, Frye looked at the Old and New Testaments as the source of eternal themes, symbols, and images that formed entire systems of metaphors that you could apply to the study of all literature. In other words: all of those motifs (or archetypes, as he called them) you find in, say, Moby-Dick (i.e., struggle between good and evil) or Uncle Tom's Cabin (i.e., Tom as Christ figure) showed up in the Bible first, and Frye wants you to know it.
Frye's big obsession was that when you read literature, you must read it as part of the grand scope of Literature. So, picture this: literature from the beginning of time and from just about every culture and language was rooted in the imagination. That means that we should read all works of literature as "drawing from the same well of myths, metaphors, hopes, dreams, fears and symbols" (source). Literature is like one big, huge, imaginative system, and you can break that system down to a number of common archetypes.
Now, don't get too carried away. When Frye says you can trace everything back to the Bible, he's not talking about sacred Yoruban poetry; he was strictly a Western canon kind of guy. He wrote his pièce de resistance, Fearful Symmetry (1947), on the poetry of the English Romantic poet William Blake, and he wrote his other masterpiece (who has two? Frye, that's who), Anatomy of Criticism (1957), on everything from Beowulf to Emily Dickinson to James Joyce to T.S. Eliot. It doesn't get a lot more Western than that.
Still not sure Frye is worth your time? Well, take a look at what he has to say to anyone who's wondering what the point of studying literature is: "The critical study of literature […] provides a basic way 'to produce, out of the society we have to live in, a vision of the society we want to live in'" (source). We can get behind that.