The best folk art is “simply art,” Don Walters writes in his introduction to Spiritually Moving , a book on American folk sculpture being published by Harry N. Abrams Inc. this month. A former curator of the Abby Aldrich Rockefeller Folk Art Center, Walters reminds us that modern artists—the sculptor Elie Nadelman, the painters Marsden Hartley and Charles Sheeler—were among the first champions of American folk art and that what drew them was its genius for abstraction, a pared-down purity they sought in their own work. With its minimal text and extraordinary photography and design, Spiritually Moving presents—with consummate artistry—one of the finest collections of folk sculpture still in private hands.