In his house in Jerusalem, Gershom Scholem, the great historian of Jewish mysticism, kept a painting, Paul Klee’s Angelus Novus. It was willed to him by a friend of his youth, the German critic Walter Benjamin. This curious work of art, with its schematic portrait of a startled angel, hair of tangled scrolls, arms spread seemingly in both recoil and benediction, was an icon of one of the more unusual friendships in 20th-century intellectual history.

The two men referred of ten in their letters to this heavenly figure. It was, for each of them, a most cherished possession. And this angel, in all its ambiguousness, also seems in retrospect to represent the larger issues of debate and discussion between these two German-Jewish thinkers in the twilight days of Germany before the advent of Hitler-a debate and discussion over just what sort of redemption could be offered to a fallen world. At a time when fascism was on the horizon and Marxism so youthfully full of great hopes, the arguments of Benjamin and Scholem ranged over the promises and dangers of religious and political idealism. They differed over the origins of the modern world itself, over how to explain its debased material and spiritual life, and over what hopes could be held out in the face of imminent catastrophe.