Allegory is a metaphor that usually teaches a lesson. Allegories have frequently been used to comment on some aspect of society in attempts to change it, admire or mock it. One of the most famous allegories is Plato’s “Allegory of the Cave” where he symbolically presents the fundamental way he believed humans experience the world and their struggle to “see” or understand Ideal Forms (Ideas and Conceptual Objects in perfect form = Ultimate Truth). Plato said that we are chained within the cave and thrice removed from the Ideal Forms.
Allegories are also ways to symbolically portray world events and are effective as a means of communicating to wider audiences by popular culture. George Orwell’s Animal Farm is an allegory of the Russian Revolution. Lord of the Flies is an allegory about the conflicts of civilization via individualism and mob mentality. There are allegories throughout most canons of literature. So, it’s important to English literature because it allows writers to creatively comment on anything from human experience to politics and so on; and popular writers will be able to share their ideas with audiences, who would otherwise only get political, experiential messages and metaphors from scientists and politicians. Allegories are a means for exploring ideas and provoking thought. Therefore, they're important for English Literature and by provoking thought, important for society, politics, culture or whatever system or object they allegorize.
Allegory can be classified under,
Figure of speech -Figure based on similarity :-
i) Simile ii) Metaphor iii) Allegory iv) Parable v) Fable
Allegory (Gk. allos, other; and agoreuo, I speak; literally, speech having a meaning other than the literal)
This is a figure of speech by which a lengthy and detailed comparison is instituted between two apparently dissimilar subjects usually for the purpose for a moral instruction. An Allegory therefore, is nothing but an elaborately worked out similitude, a detailed description of one thing under the garb of another. It differs from a simile in the fact that it presents only the secondary aspect in all its detail.
The most famous allegorical prose in English prose literature is Bunyan's "Pilgrim's Progress", where the life of a Christian is represented as a perilous journey with a happy termination. "Moby Dick" by Melville and "Old Man and the Sea" by Hemingway are some allegories of modern literature.