All talk of Ruth's modesty seems a bit silly when you realize that in Perek 2 Boaz is likely criticizing Ruth for her lack of modesty.
The verse (2:3) tells us that Ruth gleaned with the male reapers [וַתְּלַקֵּט בַּשָּׂדֶה, אַחֲרֵי הַקֹּצְרִים] and further (2:5) tells us that this breach of modesty scandalized Boaz, leading him to demand her identity [לְמִי הַנַּעֲרָה הַזֹּאת]. After the male reapers pin Ruth's blunder (2:6) on her foreign birth [וַיֹּאמַר: נַעֲרָה מוֹאֲבִיָּה הִיא] Boaz diplomatically (2:8) tries to encourage her to glean with the women instead [וְכֹה תִדְבָּקִין, עִם-נַעֲרֹתָי] She doesn't get the hint (2:21) [ גַּם כִּי-אָמַר אֵלַי, עִם-הַנְּעָרִים אֲשֶׁר-לִי תִּדְבָּקִין] and it needs to be reinforced by her mother-in-law (2:22) [טוֹב בִּתִּי, כִּי תֵצְאִי עִם-נַעֲרוֹתָיו]
However, despite this textual evidence that Ruth was simply unaware of the local Judean ideas about modesty, the lesson the Midrash shoehorns into the text is that Ruth demonstrated exemplary modesty by bending her knees to glean, and not her back, thus exposing less of her legs. (!)
TaliAdler marvelously solves all problems.
She says: That's part of the point, though. Throughout the book, people are subtly criticizing Ruth for her Moabite lack of modesty, correcting her every time she talks about gathering with the nearim. (Boaz and Noami both do that.) Ultimately, though, it's Naomi who tells Ruth to do something very immodest--dress up, perfume herself, go down to the threshing floor at night, presumably to seduce Boaz and get him to marry her. Ruth instead does that in a very modest way, not dressing up, not using physical charms, and instead speaking to Boaz directly. It's the supposedly immodest Moabite woman who ultimately values modesty in a way that Noami, a religious Israelite woman, doesn't.
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