A Better Reward

Why would Abram give up all that he had just won on the battlefield? All of the plunder, all of the people, which Abram rightly brings back, now given over to the king of Sodom; nothing kept for himself. Why? Or why would the Apostle Paul consider all of that which he was and had as rubbish? Was it not for Christ? Was it not to gain Christ? Is not Christ the Christian's great reward?