The contradictions inherent in presenting a Gandhi opera at one of the world’s most richly endowed performing-arts institutions, even as protests against income inequality erupted downtown, inspired a notable demonstration on the last night of the run. A group allied with Occupy Wall Street gathered at the edge of Lincoln Center Plaza, berating the police, Mayor Michael Bloomberg, and the right-wing billionaire David H. Koch, a Lincoln Center donor. When “Satyagraha” ended and operagoers left the Met, some defied a police barricade and joined the protest. Glass did as well, and he addressed the crowd, making use of the “human microphone” of call and response. All he did was to utter the final lines of the opera: “When righteousness withers away and evil rules the land, we come into being, age after age, and take visible shape, and move, a man among men, for the protection of good, thrusting back evil and setting virtue on her seat again.” He said those words twice more, mingled for a little while, got a cab, and went home. As in the greatest moments of his music, Glass delivered a message of awe-inspiring simplicity.