Geertz had a splendid eye for making sense of ideas and meanings — pulling out the figure from the ground. Here are a few lines on the significance of Foucault:
Foucault’s leading ideas are not in themselves all that complex; just unusually difficult to render plausible. The most prominent of them, and the one for which he has drawn the most attention, is that history is not a continuity, one thing growing organically out of the last and into the next, like the chapters in some nineteenth-century romance. It is a series of radical discontinuities, ruptures, breaks, each of which involves a wholly novel mutation in the possibilities for human observation, thought, and action…. Under whatever label, they are to be dealt with “archaeologically,” That is, they are first to be characterized acording to the rules determining what kinds of perception and experience can exist within their limits, what can be seen, said, performed, and thought in the conceptual domain they define. That done, they are then to be put into a pure series, a genealogical sequence in which what is shown is not how one has given causal rise to another but how one has formed itself in the space left vacant by another, ultimately covering it over with new realities. The past is not prologue, like the discrete strata of Schliemann’s site, it is a mere succession of buried presents. (“Stir Crazy,” 1978, 30)
This is a very concise, insightful statement of Foucault’s position, and certainly more understandable than any particular stretch of The Archaeology of Knowledge & The Discourse on Language
I have not read Foucault but like the way his thoughts are so succinctly summarized here.