Gustav Mahler’s 2nd, 3rd and 4th symphonies are his “Wunderhorn symphonies,” each using music from songs he set to texts from the three-volume collection of German poems and folk songs, “Des Knaben Wunderhorn.” While the Second symphony explores death and resurrection and the Third contemplates existence and God, all this leads up to the final movement of the Fourth symphony which features a soprano singing a child’s vision of “Das himmlische Leben” or “Life in Heaven.” Mahler’s entire 54-minute Symphony No. 4 is today’s Midday Masterpiece.