In writing there are three levels when it comes to the complexity of the thought process for both the reader and the writer. It can also be thought as the interaction between those two.
First level is simply stating the facts. There is no deeper analysis offered by the author than using their own words telling about the subject matter. The reader gets the information without any additional work and is just expected to accept the information as is.
What makes a text more interesting is offering at least some level of analysis, reflection or other digest of the information. The writer can express his own feelings and conclusions about the subject beyond just stating the facts. For the reader this can offer some controversy or agreement, but in general is still just something to consume and acknowledge.
The most challenging level to reach for a text is to make the reader think. To make them come up with their own conclusions. To reach this, a writer much know the subject well enough to be able to think about different possible outcomes the user might come up with when presented these facts. When done well, reading such text feels like a dialogue between the writer and the reader.