When China’s leader, Xi Jinping, recently warned officials to ward off the temptations of corruption and Western ideas of democracy, he cited Han Fei, a Chinese nobleman renowned for his stark advocacy of autocratic rule more than 2,200 years ago.

“When those who uphold the law are strong, the state is strong,” Mr. Xi said, quoting advice that Han Fei offered monarchs attempting to tame disorder. “When they are weak, the state is weak.”

Seeking to decipher Mr. Xi, who rarely gives interviews or off-the-cuff comments, China watchers have focused on whether he has the traits of a new Mao, the ruthless revolutionary, or a new Deng Xiaoping, the economic reformer. But an overlooked key to his boldly authoritarian agenda can be found in his many admiring references to Chinese sages and statesmen from millenniums past.