There is a sense in which narratives (stories), whether true or fictional, mean what they do as wholes, not as parts. There is a danger, as we preach, of cutting up the story into pieces in a way that obscures the big, central issues. We need to have a strong sense of the major themes in the book, and then we can decide how we'll preach from it.
However, you can preach Ruth in parts. Chapter 1, for example, is about going away full and coming back empty. In a sense, this is what the whole Bible is about: it's about the human race, who were full, going away and suffering loss, pain and death, and about God's unexpected work of salvation in bringing back his empty ones by his mercy.
But the people listening won't see why this is a proper use of chapter 1 until they reach the genealogy at the end.
Read the whole thing here.