It's easy, when you have been studying the same subject for a long time, to get used to how ideas relate and how parts of the subject relate to other parts.
Then you start writing, and you want to look at and discuss all the cool details and neat subtleties of the subject you describe. Each tree is special for its own unique characteristics and for its relationship with the other trees.
And so, you write about each individual tree. And the forest, implicit in your understanding of the project, gets little attention in the writing.
But the reader is not familiar with the forest in the way that you are. And thus may not be able to see the forest for the trees.
As the author of a long academic work (this set of comments is not appropriate for works where one might not want the reader to see the forest--like a mystery novel), you can avoid bewildering your reader by providing occasional sentences and paragraphs that help the reader orient him or herself in the forest. By reminding the reader of the current location in the argument, as well as how that part of the argument relates to the whole, then the reader begins to understand the larger structure of the argument--the reader can see the forest and understand the forest as a whole, not just as the individual trees.
The practice of putting in indications of the location in the argument is particularly useful when making transitions in the document. And a certain degree of redundancy is ok in these indications of place: you're helping the reader orient him/herself, so some reference to a familiar place is appropriate.