Meaning
Immanentize: to bring about to the immanent realm (the realm of man). Essentially, to "make really real."
Eschaton: Speculated to the be peaceful and heavenly state of humankind's future history: a true golden age before the species end.
A cross between Armageddon and "Heaven on Earth"... but, metaphorically, it could simply be viewed as a revolution, or the end of an era.
Another View
The term Eschaton refers to the end of the present world and is addressed in the study of eschatology. In the novel the idea of 'Immanentizing the Eschaton' is repeated. In political theory and theology, to immanentize the eschaton means trying to bring about the eschaton (the end of the world).