BEIJING—One Thursday morning in June, 200 senior officials crammed into an auditorium in the Communist Party’s top training academy to study a revolutionary idea at the heart of President Xi Jinping’s vision for China.

They didn’t come to brush up on Marx, Lenin or Mao, staple fodder at the Central Party School since the 1950s. Nor were they honing their grasp of the state-guided capitalism that defined the nation for the last 35 years.

They came to hear Wang Jie, a professor of ancient Chinese philosophy and a figure in the country’s next ideological wave: a renaissance of the traditional culture the Communist Party once sought to destroy.

For two hours, Prof. Wang says, he reeled off quotes from Confucius and other Chinese sages—whom the party long denounced as feudal relics—and urged his audience to incorporate traditional concepts of filial piety and moral rectitude into their personal and professional lives.

“I’m getting hoarse,” Prof. Wang says over a cup of green tea after class. The previous day, he had lectured at the culture ministry and, the day before, at the commerce ministry. Monday would be the insurance regulator. “Xi Jinping’s words,” he says, “have lit a fuse.”