Gandhi who was assassinated about 20 years before King, is telling King all that happens when they kill your body is that what you have stood for and what you have left behind for your followers lives long after your death. Not to worry is the message: all will come out well when the methods you have used sink in to the leaders and followers you have left behind.
All that happens is that those who oppose you enough to kill you will think you are dead: you are not. Your legacy becomes stronger and stronger.
