The short book of Ruth is a bridge between the two major parts of Israel’s covenant history. The first part (Genesis–Judges) focuses on how Abraham’s descendants became a nation and on the covenant God made with Israel. The second part (Samuel–Kings) tells the story of the nation’s kings and the covenant God made with David as the head of Israel’s royal line. Ruth helps the transition by opening in the days of the judges and ending with the genealogy of David.
The book appears to have been written to defend David’s right to be king. He was the great-grandson of a Moabite named Ruth. Because the people of Moab didn’t help the Israelites when they came out of Egypt, the law didn’t permit any descendant of a Moabite to join Israel, down to the tenth generation. If they couldn’t even join the community, how could one of them serve as king?
The book is set up like a drama or stage play. Each scene features a short introduction and then dialogue between the characters. The book ends with a ten-generation genealogy leading up to David. So the form of the book mirrors its purpose, which is to show that genuine faith was present in a woman from a nation whose descendants were normally excluded for ten generations.
The book also shows how God’s purposes are accomplished in the world. God’s good laws (allowing the poor to collect grain in the fields), his providence over events, and the personal kindness of people all combine to help the story find a redemptive conclusion.