The Unknown Light: The Poems of Fray Luis de Leon. Translated by Willis Barnstone. Published by State University of New York Press in 1979.

Introduction and translation by Willis Barnstone. During Spain's Golden Age, Fray Luis de Leon wrote mystical poems which prompted Cervantes to proclaim Leon "a genius who astounds the world and who, in ecstasy, might rob us of our senses."

Leon was also an active man who taught at the University of Salamanca, translated classical and biblical literature, and wrote on religious themes. Twice denounced before the Inquisition, he was imprisoned for "heresy," though he returned to the University to later hold the chairs of Moral Philosophy and Biblical Studies. Tradition has it that he began his lecture the first day after returning from four years' imprisonment with the words "As we were saying yesterday...."

The mysticism of his poems, contends translator Willis Barnstone, has not been adequately appreciated because critics have been distracted by Leon's other achievements and battles and because they have worked with too narrow a definition of mysticism.

In his introduction Barnstone compares Leon with other Spanish mystical poets and explains the Christian, Judaic, and Islamic influences on Spanish mysticism. He discusses the varieties of mystical experience and provides the context for understanding Leon's mysticism, concluding, "Who is Luis de Leon? Look at the poems. He is there."