Ruth was a Moabite woman who married Mahlon, the son of Naomi. Naomi, an Israelite, lived in Moab with her husband Elimelech and their two sons. After Elimelech's death, the sons both married Moabite women. Tragically, Naomi's sons died and she decided to return to Israel. When she bid farewell to her daughters-in-law, Ruth insisted that she accompany her back. Naomi tried to persuade her otherwise.
But Ruth replied, "Don't urge me to leave you or to turn back from you. Where you go I will go, and where you stay I will stay. Your people will be my people and your God my God. Where you die I will die, and there I will be buried. May the LORD deal with me, be it ever so severely, if anything but death separates you and me." (Ruth 1:16-17)
When Naomi realized that Ruth couldn't be dissuaded, they returned together to Bethlehem, the old home from which Elimelech had migrated. There she had a rich relative, Boaz, to whom Ruth was eventually married.
Ruth became the mother of Obed, the grandfather of David. Thus Ruth, a Gentile, is among the maternal progenitors of Jesus.
The story of "the gleaner Ruth illustrates the friendly relations between the good Boaz and his reapers, the Jewish land system, the method of transferring property from one person to another, the working of the Mosaic law for the relief of distressed and ruined families; but, above all, handing down the unselfishness, the brave love, the unshaken trustfulness of her who, though not of the chosen race, was, like the Canaanitess Tamar (Gen. 38:29; Matt. 1:3) and the Canaanitess Rahab (Matt. 1:5), privileged to become the ancestress of David, and so of 'great David's greater Son'" (Ruth 4:18-22). [Easton's Bible Dictionary]