Good writing sticks around in your mind. Perhaps it may be difficult to summarize; even if it’s long, it is probably as tight as it could be already. 

Once you read it, even if you don’t fully consciously “get it,” you can’t go back; you start seeing what the writer is saying.

I recently read a metaphor likening writing to furniture; I’ve lost the source, so I can only make a best guess (which is where creativity has an opening to come in). Perhaps it was more like a character coming in and kicking around the metaphorical furniture in your mind. 

Or perhaps writing is the furniture, and it needs you to make space for it in the space of your mind.