I admire the imagination and skill of a writer, capable of writing such an epic book. A tremendous work by all means - not only because of the number of pages, the complexity of characters and multitude of stories, but also the topics covered.
"Purity" is hard to grasp at first because of its fragmentation. Only after you laboriously detangle all the threads, the full impact of the book can be felt. An impact so big for me that I think it will take time to "digest" and it will haunt me for days with unresolved moral dilemmas.