{N}3,{/}1: Why does Ruth want to have Boaz for her husband? In order to follow the so-called "Levirate" law, mentioned in chapter 38 of Genesis.
When a man dies without leaving children, the sacred duty of his widow is to marry the nearest relative of her deceased husband. The first son she would bear him would take the name of the dead man and be considered his son.
This explains Ruth's sacrifice. She gives up marrying a young man and accepts being the wife of an older and foreign man, because this can give her a son "for" her dead husband. Thus Ruth fulfills the mysterious plan of God who predestined her to be among Christ's ancestors (see Mt 1:5).

