In political theory and theology, to immanentize the eschaton means trying to bring about the eschaton (the final, heaven-like stage of history) in the immanent world. It has been used by conservative critics as a pejorative reference to certain projects perceived as utopian, such as socialism, communism, and transhumanism. In all these contexts it means "trying to make that which belongs to the afterlife happen here and now (on Earth)" or "trying to create heaven here on Earth." Theologically the belief is akin to Postmillennialism as reflected in the Social Gospel of the 1880-1930 era, as well as Protestant reform movements during the Second Great Awakening in the 1830s and 1840s such as abolitionism.
Modern usage of the phrase started with Eric Voegelin in The New Science of Politics in 1952. Conservative spokesman William F. Buckley popularized Voegelin's phrase as "Don't immanentize the eschaton!" Buckley's version became a political slogan of Young Americans for Freedom during the 1960s and 1970s.
Voegelin identified a number of similarities between ancient Gnosticism and the beliefs held by a number of modernist political theories, particularly Communism and Nazism. He identified the root of the Gnostic impulse as social alienation, that is, a sense of disconnection from society and a belief that this lack of concord with society is the result of the inherent disorder, or even evil, of the world. He described this alienation as having two effects:
One of the more oft-quoted passages from Voegelin's work on Gnosticism is that "The problem of an eidos in history, hence, arises only when a Christian transcendental fulfillment becomes immanentized. Such an immanentist hypostasis of the eschaton, however, is a theoretical fallacy."