During the time of the Judges when there was a famine, an Israelite family from Bethlehem - Elimelech, his wife Naomi, and their sons Mahlon and Chilion - emigrate to the nearby country of Moab. Elimelech dies, and the sons marry two Moabite women: Mahlon marries Ruth and Chilion marries Orpah. The two sons of Naomi then die themselves. Naomi decides to return to Bethlehem. She tells her daughters-in-law to return to their own mothers, and remarry. Orpah reluctantly leaves; however, Ruth says, "Entreat me not to leave you, or to turn back from following you; For wherever you go, I will go; And wherever you lodge, I will lodge; Your people shall be my people, and your God, my God. Where you die, I will die, and there will I be buried. The LORD do so to me, and more also, if anything but death parts you and me." (Ruth 1:16-17 NKJV) The two women return to Bethlehem. It is the time of the barley harvest, and in order to support her mother-in-law and herself, Ruth goes to the fields to glean. The field she goes to belongs to a man named Boaz, who is kind to her because he has heard of her loyalty to her mother-in-law. Ruth tells her mother-in-law of Boaz's kindness, and she gleans in his field through the remainder of the harvest season. Boaz is a close relative of Naomi's husband's family. He is therefore obliged by the levirate law to marry Mahlon's widow, Ruth, in order to carry on his family line. Naomi sends Ruth to the threshing floor at night and tells her to "uncover the feet" of the sleeping Boaz. Ruth does so, Boaz awakes, and Ruth reminds him that he is "the one with the right to redeem." Boaz states he is willing to "redeem" Ruth via marriage, but informs Ruth that there is another male relative who has the first right of redemption. The next morning, Boaz discusses the issue with the other male relative before the town elders. The other male relative is unwilling to jeopardize the inheritance of his own estate by marrying Ruth, and so relinquishes his right of redemption, thus allowing Boaz to marry Ruth. Boaz and Ruth get married and have a son named Obed (who by levirate customs is also considered a son or heir to Mahlon, and thus Naomi's grandson). In the genealogy which concludes the story, it is pointed out that Obed is the descendant of Perez the son of Judah, and the grandfather of David. David is the ancestor of Jesus Christ.

Two major theological themes in the Book of Ruth are redemption and hesed (see below). Redemption was both a rich social and religious concept in the daily life of Israelites, and they were aware of their social responsibility to one another to protect the weak and unprotected. Redemption secures the life of the people as a community, not just as individuals. The marriage of Boaz and Ruth was of a type known as a levirate marriage. Redemption[13][14] is a feature of levirate marriage, and it is a duty taught in Deuteronomy (25:5-10). This custom required a close relative to marry the widow of the deceased (the kinsman) in order to continue his family line. Interestingly, Ruth is not Elimelech’s widow and Boaz is not his brother. Therefore, some scholars refer to Boaz’ duty as “levirate-like” or as a "kinsman-marriage."[15] Moreover, the Israelites understanding of redemption included both that of people and of land. In Israel land had to stay in the family. The family could mortgage the land to ward off poverty; and the law of Leviticus 25:25ff required a kinsman to purchase it back into the family. The kinsman, who Boaz meets at the city gate, first says he will purchase the land, but upon hearing he must also take Ruth as his wife he withdraws his offer. His decision was primarily a financial decision since a child born to Ruth through the union would inherit Elimelech’s land, and he would not be reimbursed for the money he paid Naomi. Boaz becomes Ruth and Naomi’s "kinsman-redeemer." [16] The Israelites' understanding of redemption is woven into their understanding of Yahweh. God stands by the oppressed and needy. He extends his love and mercy offering a new freedom and hope. God has a deep concern for the welfare of his people, materially, emotionally and spiritually. The redemption theme extends beyond this biblical book through the genealogy. First, in Ruth 4:13 God made her conceive. Second, through the genealogy it is shown that the son born to Naomi is more than just a gift from God to continue her lineage. The history of God’s rule through the David line connects the book’s theme in to the Bible’s main theme of redemptive history. Hesed, sometimes translated as "loving kindness," also implies loyalty. The theme of hesed is woven throughout Ruth, beginning at 1:8 with Naomi blessing her two daughters-in-law as she urges them to return to their Moabite families. She says, “May the Lord deal kindly with you, as you have dealt with the dead and with me.” Both Ruth and Boaz demonstrate hesed to their family members throughout the story. These are not acts of kindness with an expectation of measure for measure. Rather, they are acts of hesed that go beyond measure and demonstrate that a person can be required to go beyond the minimum expectations of the law and choose the unexpected. However, the importance of the law is evident within the Book of Ruth, and the story reflects a need to stay within legal boundaries. Boaz, in going beyond measure in acquiring the property (demonstrating hesed), redeems not only the land but both Naomi and Ruth as well. The two widows now have a secure and protected future.