Historians like to describe the last two centuries of painting as less of an act and more of a reaction. Impressionism, modernism, surrealism, the whole of abstraction — they’re all a rejection and reinterpretation of the art that came before them; art that embraced formalism and natural beauty, that ennobled the upper classes and exalted sacred icons, that valued composition above all else. In that way, the 60 objects in “Treasures of British Art” are important not just for what they are, but also for what they wrought.