In this section of Ruth we see Boaz doing mitzvot (good deeds) beyond the mere obligations of Torah. The rabbis see in the teaching of Torah a command to go beyond obligation, especially Leviticus 19 — the chapter on neighbor-love, care for resident aliens like Ruth, and the gleaning law.
The injunction of Leviticus 19:2 (“holy you will be since holy am I”) is explained by the rabbis in a number of ways. In relation to Boaz’s action on behalf of Ruth and Naomi, the most relevant aspect of holiness is the sense of excess in performing positive commandments. A famous and simple illustration is found in Sifra (an early midrash collection, probably 3rd century CE): “It is like the court of a king; what is the court’s duty? To imitate the king!” (cited in Milgrom’s commentary on Leviticus 17-22). And in Deuteronomy 10:18-19 we read that God “upholds the cause of the widow and fatherless” and thus “you too must befriend the resident alien (sojourner).”
Boaz’s extraordinary care for Ruth — the widow and also resident alien — and his relative’s widow Naomi is beyond the requirements of the gleaning law. The amount of help one must give to a resident alien is unspecified. Boaz shares with Ruth at the table his parched grain and gives her vinegar to dip her bread in. He does more than give a hungry sojourner bread, but embellishes her meal with pleasantness in imitation of God, who gives generously and delights the heart of those who hold him in awe.