The famine in Judah had driven Elimelech and his family to Moab. To Moab? Moab, the enemy of the Israelites as they entered into the Promised Land. Moab's king, Balak, was the one who hired Balaam to curse them (although that didn't work out the way Balak wanted; see Numbers 22-24.) After settlement, Moab was still their enemy. Under King Eglon, Moab controlled the Israelites for eighteen years (see Judges 3 for how this ended.)
Elimelech took his family to Moab. The place that has been your enemy has become your refuge. His sons married wives from Moab. Enemies become rescuers. Enemies become relatives.
Elimelech and his two sons die. His wife realizes that she has to go back to Judah. Her Moab family are daughters, and it is sons who have the responsibility to care for widows. She advises her widowed daughters-in-law to return to their families where they will have a chance of getting remarried.
One takes her advice. The other, Ruth, does not.
Ruth, the Moabite, refuses to abandon her mother-in-law even if that means she will have to go to a country that has been her country's enemy, even if it means giving up her family.
Phyllis Trible points out that only Abraham had made this radical a move.
Allen & Williamson in their Preaching the Old Testament, stress the importance of covenant. Having made covenant with her husband, Ruth has now extended covenant to her mother-in-law and to what is her mother-in-law's. They ask:
What would it take for today's congregation to make a Ruth-like commitment to the Naomis of the world?