Ruth 2:20 And Naomi said to her daughter-in-law, “May he be blessed by the Lord, whose kindness has not forsaken the living or the dead!” Naomi also said to her, “The man is a close relative of ours, one of our redeemers.”

Redeemer has multiple meanings in Jewish tradition. Here the word is  gâʼal, gaw-al’; a primitive root, to redeem (according to the Oriental law of kinship), i.e. to be the next of kin (and as such to buy back a relative’s property, marry his widow, etc.) Boaz being a kinsman saw honor in Ruth.

Ruth 3:10 And he said, “May you be blessed by the Lord, my daughter. You have made this last kindness greater than the first in that you have not gone after young men, whether poor or rich.

The tradition of taking a kinsman’s widow as a wife is ancient in Jewish tradition.

Genesis 38:6-11 English Standard Version

6 And Judah took a wife for Er his firstborn, and her name was Tamar. 7 But Er, Judah’s firstborn, was wicked in the sight of the Lord, and the Lord put him to death. 8 Then Judah said to Onan, “Go in to your brother’s wife and perform the duty of a brother-in-law to her, and raise up offspring for your brother.” 9 But Onan knew that the offspring would not be his. So whenever he went in to his brother’s wife he would waste the semen on the ground, so as not to give offspring to his brother. 10 And what he did was wicked in the sight of the Lord, and he put him to death also. 11 Then Judah said to Tamar his daughter-in-law, “Remain a widow in your father’s house, till Shelah my son grows up”—for he feared that he would die, like his brothers. So Tamar went and remained in her father’s house.

We find Tamar in the lineage of Jesus even though Judah’s son had died. Matthew 1:3 and Judah the father of Perez and Zerah by Tamar, and Perez the father of Hezron, and Hezron the father of Ram,

Shelah did not take Tamar to wife, so Tamar played the harlot to Judah after his wife died and tricked him into redeeming her. So strong is this tradition of the Jews that a widow should have a son to care for her in her old age that Jesus gave His mother to John because all her kinsmen would die and she would be left without a son.

John 19:26-27 English Standard Version

26 When Jesus saw his mother and the disciple whom he loved standing nearby, he said to his mother, “Woman, behold, your son!” 27 Then he said to the disciple, “Behold, your mother!” And from that hour the disciple took her to his own home.