The Book of Ruth could have finished after the beginning of chapter 4 - Boaz has redeemed Ruth and all that's left is happily ever after. However, the story actually continues and gets better. The redemption of Ruth is not limited to her life, but actually extends through her line and legacy.
What's a legacy? Put simply, it is the inheritance you pass on to future generations. All of us have a mixed influence of both generational sin and generational blessing. The end of Ruth shows how God redeems legacy and how we can pass on blessing to future generations. While the past has shaped your present, it doesn't have to shape your future - there is redemption in Jesus.