It’s one of the most important skills in the storytelling aspect of writing novels. Alas, it is often ignored for its more flashy cousins but it's important in many ways.
When writers talk about progression of a plot or, for that matter, progression of a character arc, they’re talking about the steps of plot or character that lead the reader to a satisfying ending. If you can create foreshadowing, that is give the reader of hint of what is to come, and then build what is to come in an interesting way, that’s an important part of plot progression.
I work on foreshadowing the most after I have a workable draft (maybe my second or third) and know where my ending of various plots are. Some of my minor plots may finish before the end of the manuscript, but the most important ones are at the end and will require several steps. If I can foreshadow at least some of these steps as I move the novel forward, I'll create suspense and that sense of progression and, perhaps that satisfying payoff. Another way to say this: the foreshadowing helps me lay out the breadcrumbs that the reader will follow to the destination, the conclusion of the novel.
Hope this is helpful.
Happy Writing Fellow Campers—