In Emily Rapp’s powerful new memoir, “The Still Point of the Turning World,” the “worst possible news” arrives right in the second sentence: “our son, Ronan, then nine months old, had Tay-Sachs disease, a rare, progressive and always fatal condition with no treatment and no cure.”

But you should keep reading. Rapp has written a beautiful and passionate elegy for her son, a book that offers deep wisdom for any reader. In poetic language that is always grounded in the reality of her family’s day-to-day effort to cope with unimaginable pain, Rapp journeys through the terror of hearing Ronan’s diagnosis — “his death sentence, really” — to the slow, painful acceptance of death: