Walking in the woods near his country house one night in January 1970, Norman Podhoretz had an epiphany. Against the evening sky, he later recalled, he saw “a kind of diagram that resembled a family tree. And it was instantly clear to me that this diagram contained the secret of life and existence and knowledge.” Podhoretz compared his vision to a verse by the seventeenth-century English poet Henry Vaughan that began, “I saw eternity the other night.”

Just turned forty, Podhoretz was completing his first decade as the editor of the prestigious liberal monthly Commentary. By all appearances, he was still a liberal Democrat and a secularist, not exactly the type to undergo a quasi-religious experience. Though educated in the essential Hebrew and Jewish texts, he was not particularly drawn to synagogue Judaism or to political Zionism. But now, according to his own testimony, he...