If you haven’t yet read the Divine Comedy—you know who you are—now is the time, because Robert and Jean Hollander have just completed a beautiful translation of the astonishing fourteenth-century poem. The Hollanders’ Inferno was published in 2000, their Purgatorio in 2003. Now their Paradiso (Doubleday; $40) is out. It is more idiomatic than any other English version I know. At the same time, it is lofty, the more so for being plain. Jean Hollander, a poet, was in charge of the verse; Robert Hollander, her husband, oversaw its accuracy. The notes are by Robert, who is a Dante scholar and a professor emeritus at Princeton, where he taught the Divine Comedy for forty-two years.