Annual plenums are the mechanism through which the 95-million-member party defines the parameters of official ideology, political discourse and policy direction. But this plenum was different. It’s the first time since the era of Deng Xiaoping that the party has produced a formal resolution on party history, which now officially defines Mr. Xi’s political position within the Chinese Communist pantheon.

There have only been three such resolutions in the party’s 100-year history. and they are always major, epoch-defining events. With this resolution the party has elevated Mr. Xi and “Xi Jinping Thought” to a status that puts them beyond critique. Because both are now entrenched as objective historical truth, to criticize Mr. Xi is to attack the party and even China itself. Mr. Xi has rendered himself politically untouchable.

In the hard world of political practice, this has five implications. First, Chinese Communists, as historical materialists, have an ideological fetish for periodizing, trying to identify where they are in their relentless march toward a socialist society and the restoration of China as the most powerful country on earth. Officially, there are now three periods in Chinese Communist history: the Mao Zedong era, when China restored national unity and expelled foreign colonialists; the Deng era, when China became prosperous; and now the Xi era, when China is to become globally powerful.

Second, the resolution reconfirms Mr. Xi’s position as the core of party leadership and emphasizes that this is of “decisive significance”—a critical phrase—for China.