It’s a practice and a tool which aims to extract the maximum value from the fiction and to make knowledge better grounded, i.e., less purely abstract and more sensory, more easily recalled, and more practicable. It means that every novel read, you not only gain enjoyment, but an improved ability to perceive the world.
The essay is personal compilation of snippets, scenes, quotes from a novel that concretely embody a principle you have already thought through. The approach is premised on a philosophic view on the nature of art and its role in man’s life: that the artist is like a god breathing life into the nostrils of an inert clay figure that is an abstraction; and that man, to properly grasp abstractions, requires the guidance and selective attention of artists embodying abstractions in concretes.
It is not necessarily an extraction of what the artist intended, but what implicitly or explicitly stands out to you in a particular character or scene.