It's a story about God and how he restores those who look to him with hope. It's about God's covenant faithfulness and it contributes to the overall covenant storyline that unifies the entire Bible. The author has gone to great care to honor Ruth, Naomi, and Boaz through the development of their characters in the story.
They are character studies of how God works in mundane, everyday events in the lives of his people (and what human covenant faithfulness looks like in return).
The story of Ruth begins with a reminder of the dark and difficult days of Israel. The father of a family dies while in Moab and his two sons marry Moabite women, Ruth and Orpah. Their husbands die, and when Naomi announces she is returning to Israel, Ruth chooses to go with her. Orpah chooses to stay in Moab but Ruth shows great loyalty to Naomi by saying, Where you go, I am going. Your people will become my people and your God will be my God."
Upon arriving in Israel, the two women find a farmer who allows them to pick grain in his field. Boaz is a man of noble character and makes special provisions for Ruth. Realizing they are related to Boaz, Ruth calls him their family redeemer."
Ruth decides to quit wearing the clothes of a widow, lets Boaz know that she is available to be married, and asks him if he is willing to redeem Naomi's family by marrying her. Boaz is amazed at Ruth's character and is glad to take her as his wife.
Just as Ruth was loyal to Naomi in chapter one, Boaz is loyal to Naomi's family in chapter four. The story concludes with reversal of the tragedies it began with. Ruth marries Boaz and gives birth to a son. This story is marked by the little mention of God by name while showing God at work in the interconnected lives of Naomi, Ruth, and Boaz. Chapter one opens with tragedy and death, but chapter four ends with joy and birth.
Boaz and Ruth's son is named Obed. He becomes the grandfather of King David. Since Christ's lineage was of David, we see God's ultimate plan being made possible through the loyalty and faithfulness of an Israelite farmer and a Moabite widow.