In the world premiere of The Brightness of Light, by Kevin Puts, Renée Fleming and Rod Gilfry team up as Georgia O’Keeffe and her husband, Alfred Stieglitz, in excerpts from their letters. The program begins with Elgar’s Enigma Variations, in which the conundrums of the creative life hover beneath the purely instrumental surface. Andris Nelsons conducts. —M.G.