The world is a fortunate place when there are two people alive -- at the same time -- who understand Plato. Eric Voegelin was clearly one of those people in the twentieth century. This material was originally published as Volume 3 of Order and History, the core of the magnus opus that Voegelin chose to publish during his life time.
I met Eric Voegelin once as a graduate student, and asked him, "why'd you publish all this stuff?" I've been digesting his answer ever since. It was "to resist totality and totalitarianism."
Particularly, seen from this standpoint, a clear core of this book is his articulation of the Platonic concept of "metaxy," or the in-between character of life. In philosophical terms, this refers most directly and fully to "in-between" the Agathon (e.g., see myth of the cave and the Divided Line in the Republic) and the apeiron (explored most directly and deeply in the Timaeus). For the philosophically uninitiated, it is possible to speak of this in more mundane terms.
An unstated corollary of Plato's notion of the "metaxy" is that life is always larger than our categories. From a Socratic/Platonic perspective, this may include but will entail more than the epistemological recognition that every way of seeing is a way of not seeing. The notion of the "metaxy" is most fundamentally a linguistic indice pointing to ontological plenty as the ground of life, albeit lived within bounds of existential scarcity. This is a notion commonly shared by the great civilizations of East and West. The notion of the "metaxy" underscores that life is lived within a tension between the "transcendent" and "immanent" dimensions of being.
When we lose track of this tension, as we have to a great extent in the modern world, and subscribe to reductive ideological notions/understandings of life -- and most particularly, when we imagine that we can encapsulate life within the pride of our own "enlightened" categories -- on a political plane, there may be little to constrain the prideful actions of ideologies, irrespective of whether their clothing is Red or Black, or whether it is "left" or "right." Irrespective of the political stripe, repression and murder become "justified" in the pursuit of an ideological aim -- which in Voegelin's philosophical terms is to dissolve the "metaxy" in the usual modernist mode, through immanetizing the transcendent "eschaton."
Voegelin's philosophical terms may sound remarkably abstract to the modern ear (recall Robert Dahl's silly review of Voegelin's The New Science of Politics for the American Political Science journal). Facile critiques such as Dahl's typically focus on the unfamiliar language while overlooking the elementary fact that what Voegelin is asking us to do in every aspect of his work is to take a journey that precisely allows us to see the world in terms other than that of our inherited climate of opinion. For those willing to be thorough scholars rather than merely play at it within the context of given suppositions, Voegelin's scholarship offers new vistas and incredibly rich fields of study. His scholarship offers the capacity to reflect upon and act in the world in a substantively grounded mode with implications for every discipline (see e.g., A.G. Ramos' New Science of Organizations).
I submit that a key to understanding this text and the greater body of his work at large is to grasp the central significance of the "metaxy" -- not as a concept within the history of ideas -- but as a life referent of perennial relevance to the recurring challenge of resisting sophistic pretensions and the inherited or emergent ideologies of any time and place.
This text demands a great deal. You'll develop insights into Plato and Aristotle available no where else. But for Voegelin, such studies were never a matter of antiquarian interest. They were a matter of developing meaningful referents for life. The value in this text is precisely in its yield, capable of resonating throughout your life and offering far more than the initial effort it will require of you.