As far as the difference between an allegory and metaphor is worried, both equally manage to belong to the same group of figures of speech. The explanation is the fact both suggest comparison. Se trata de un procedimiento ampliamente utilizado tanto en el lenguaje literario (sobre todo en la poesía), https://juliuslrwzd.law-wiki.com/1463538/not_known_factual_statements_about_metafora