The big theme here is “kindness”. Ruth is a Moabite, so the immediate connection is to the Deuteronomy 23 prohibition of the Moabites within the congregation because of their lack of “kindness” to Israel. If not clear enough, the writer also mentions leaving Bethlehem (house of bread) for Moab, again tying back to the Moab story, where the Moabites withheld bread from Israel.
This also goes back deeper into the origin of Moab. The Boaz/Ruth threshing floor scene reminds us of scene with Lot and his daughters. Both times the man (Lot/Boaz) is drunk. Both times the women (Ruth/daughters) are looking to preserve the family line.
The story also reminds us of Judah and Tamar – again because of Tamar’s need to preserve the family seed – but also because of the connection between Judah and Boaz. Both of them have an encounter with a widow, and both have a family duty to fulfill.
The author of Ruth wants us to see the backstory of the relationship between Moab and Israel, and the familial duty of Israel. So Ruth is a redux in which the story has a different outcome – as the current actors course-correct the sins of their ancestors.
Upon entering the land, Lot (Ruth) refuses to separate from Abraham (Naomi) as was done in the past (Genesis 13). In a time of need, the Moabites (Ruth) bring Israel (Naomi) bread, displaying kindness. The widowed/barren/bereft daughter (Ruth) does not deceive to be filled, and instead trusts in the provision of the LORD. Presented with a needy/seductive woman, Israel (Boaz) happily pursues the responsibility of headship.