What does Ruth 2:21 mean?

Ruth is explaining to Naomi what Boaz told her. She asked permission to glean from his fields, but he did much more (Ruth 2:4–16). This is private conversation with her mother-in-law, but the narrator reminds the audience of Ruth's status as a foreigner. Even though she is Naomi's daughter-in-law, and Naomi calls Boaz "our" redeemer (Ruth 2:20), Ruth is still a foreigner.

The inclusion of Ruth's nationality emphasizes Boaz's kindness toward her. That's magnified further because she was originally a native of Moab (Deuteronomy 23:3–6). Boaz had his harvesters pull stalks of barley out of their own bundles for Ruth to pick up, told her to drink the water his servants provided, and invited her to eat with him and his servants (Ruth 2:9, 14–16). Boaz has determined that God's curse on the Moabites obviously doesn't apply to such a loving, noble, self-sacrificial woman (Ruth 2:11–12).

To top it all off, this isn't just a one-day provision. Ruth will continue throughout the month-long barley harvest and the following month-long wheat harvest (Ruth 2:23). In less than one day, Ruth manages to bring back grain the equivalent of two weeks' worth of pay; at this rate, by the end of the wheat harvest, she and Naomi will have what they need for a year and a half.

Except for the duration of the legal proceedings in chapter 4, this is the last time Ruth is referred to as a Moabitess. She transitions to a Bethlehemite in the two months of the harvest.

The wording here is problematic. Boaz told Ruth to stay close to his "young women" (Ruth 2:8) and said he ordered his "young men" to leave her alone (Ruth 2:9). The ESV translates Ruth's quote of Boaz as "You shall keep close by my young men." The Hebrew, however, merely means "servants" and includes women, as the NASB says. Either way, Naomi quickly corrects Ruth; Ruth is to stay near the young women, not the men (Ruth 2:22).