The Hebrew word for kinsman-redeemer is goel, and involves the redemption of property. It has nothing to do with marriage. If a Hebrew fell on hard times and had to sell property, one of his relatives should purchase that property to keep it in the family (Leviticus 25:23-25). That relative was called goel, a kinsman-redeemer. He would keep and work the land until the original owner could repurchase it or until the year of Jubilee, when it would revert in ownership to the original family. Any relative could do this, but closer relatives were allowed first choice in redemption.
We assume Naomi had the right to sell that property as Elimelech's widow. The ancient custom was for a groom to pay a bride-price (mohar) upon marriage to his wife's family. In time, this led to a major social problem: many young men could not afford the dowry and had to postpone marriage. So a marriage contract (ketubah) was developed in which an amount was stipulated, a kind of lien, to be paid to the woman by the husband in case of divorce or by his estate in the case of death. In effect, the contract assured the woman's family that she would be cared for in the event of her becoming a widow. And it was recognized that a widow could sell her husband's estate to cover her ketubah. (See Ketubot, 104.) These practices and rulings are fair, humane, and deeply sensible; we have to believe godly people in the days of Naomi had similar customs for the protection of widows.
But Naomi is a godly woman, thinking far beyond her own needs. She is thinking of the line of her husband Elimelech and sons Kilion and Mahlon. She is thinking of Ruth, who needs a husband, a home, a family, an estate. If she could get Ruth married to the kinsman-redeemer, the line of her husband would be continued through Ruth and the estate would remain in the family. The family would be merged with that of the kinsman-redeemer, but it would endure. Ruth would have a husband; Naomi would have grand-children; and yes, Boaz is the head of the ruling family of the tribe of Judah!
Here it gets a little tricky. Deuteronomy 25 states the custom clearly: a brother is to marry his brother's widow to continue the line. There are no brothers left to Naomi and Ruth. Kinsman-redeemers are not required to marry widows in Leviticus 25. The estate can be sold and redeemed, and Ruth left out of the bargain. However, should a kinsman-redeemer marry Ruth before the estate is sold, it would be de facto a claim on the estate because of Ruth's claim on the estate.
Our remedies oft in ourselves do lie, Which we ascribe to heaven: the fated sky Gives us free scope, only doth backward pull Our slow designs when we ourselves are dull.
Shakespeare, All's Well that Ends Well, 1.1.209
The plot is forming, by design on earth and heaven. Boaz is a kinsman-redeemer. He could marry Ruth and continue the line of Elimelech by merging the families in his child with Ruth. In doing so he would be in effect redeeming the estate. He has already shown interest in Ruth - he sees her with compassion and admiration. Surely these are embers that can be stoked into romantic flame.
But life is never that easy. There is another closer relative, who shall remain unnamed. If Boaz marries Ruth and lays claim to the estate, relative so-and-so could cry “foul” and demand his rightful claim to the estate. Boaz could take the woman; he would take the estate. All would be fine for Boaz and Ruth, but the line of Elimelech would lose the land.
Naomi here must trust Boaz. As head of the ruling family, when issues arose, he would sit at the gates of the city and pass judgment with the elders of the people. In helpful Rabbinic terms, he was the head of the council (bait din), and routinely offered up rulings (psak din) accepted by the community and future generations.
Boaz would need to make the following case: while Deuteronomy 25 mentions only brothers, it is not outside the spirit of the law (lifnim mishuras hadin) to rule in this situation that, while there are no brothers to carry on the line of Elimelech, since the widows are in need and the land for sale, the kinsman-redeemer should marry the widow. It is hard to imagine anyone resisting that ruling. It is wise and compassionate. But he would have to make it.
So Naomi sets her plan in action. Ruth is cleaned up, perfumed, and briefed. She forces the hand of Boaz by proposing marriage. (Yes, the woman asks the man! Chivalry is dead!) Being a cunning soul, Naomi picks the dead of night for Ruth's gambit. Some sorely want to read sauce and sizzle between the lines, but we need not turn Ruth's proposal into an immoral act. It could have been as simple as the text records. When she utters the word, “Spread the corner of your garment over me,” she is proposing marriage; when she adds the word, kinsman-redeemer,” he is fully aware that property and the line of Elimelech is involved.
The die is cast. He is flattered. He is thrilled. And in the words of Naomi, “The man will not rest until the matter is settled today.”