Qin Zheng already knew what his fate would be. Before his life ended, he still felt reluctance in his heart. He knew he couldn't compare to Qin Yuanfeng, but he didn't want to admit this. Hence, he made such a request.
He hoped that his son was able to fight against Qin Yuanfeng's son. This would be a battle of destiny, all his hopes were on it. If Qin Dangtian could win, he would feel gratified in his heart. He would die knowing that Qin Yuanfeng's son ultimately was still inferior to his son. He wouldn't have lost to Qin Yuanfeng so badly.