When Naomi returns to Bethlehem, she complains to the townspeople "I went out full, and God brought me home empty." [1:21 "אֲנִי֙ מְלֵאָ֣ה הָלַ֔כְתִּי וְרֵיקָ֖ם הֱשִׁיבַ֣נִי יְהוָ֑ה"]. This is curious, for two reasons:
(1) She wasn't "full" when she departed Bethlehem. She left during a famine.
(2) She's not "empty" now; Ruth is at her side.
The Rabbis address the anomaly by suggesting Naomi was pregnant when she left Bethlehem. They also suggest that Naomi and her husband were very wealthy when they arrived in Moab, and that she became destitute after being widowed. Notably, neither Naomi or the Rabbis seem to take notice of Ruth.
Later in the story, after Ruth has spent the night in Boaz's barn, she returns to her mother-in-law with six measures of barley, and says: "He gave me these six measures of barley saying "Don't go empty to your mother in law" [3:17 "שֵׁשׁ־ הַשְּׂעֹרִ֥ים הָאֵ֖לֶּה נָ֣תַן לִ֑י כִּ֚י אָמַ֣ר אַל־ תָּבֹ֥ואִי רֵיקָ֖ם אֶל־ חֲמֹותֵֽךְ"] In the text, Boaz says nothing of the kind. The idea that she was sent back to Naomi, carrying a heavy load of barley, so as not to return "empty" appears to be Ruth's own invention.
Perhaps Ruth uses this word because she remembers what Naomi said to the townspeople on the day of their return to Bethlehem. Naomi felt abandoned by God; now, with the use of the word "empty" [=רֵיקָ֖ם] Ruth is letting her mother in law know that the era of abandonment is over. Boaz has taken notice of them, and though God sent them back "empty" to Bethlehem, Boaz is going to correct that and restore what was lost.
It's also possible that there's a bit of foreshadowing here. Ruth is carrying "seeds" that Boaz gave her, but instead of keeping them for herself, she voluntarily gives them to Naomi. There's a double entendre here. At then end of the story Ruth does the same with her son Oved, the product of Boaz's "seeds." [4:17: וַתִּקְרֶאנָה֩ לֹ֨ו הַשְּׁכֵנֹ֥ות שֵׁם֙ לֵאמֹ֔ר יֻלַּד־ בֵּ֖ן לְנָעֳמִ֑י / "And the neighbor women said [about Oved], and gave him a name: "A son has been born to Naomi"]. As we have seen, the Rabbis said Naomi's first chapter "emptiness" referred to a lost pregnancy. By making a gift of the seeds Boaz gave her while referencing her mother-in-law's "emptiness" Ruth is symbolically handing over her children and repairing the "emptiness". The Rabbis understood this, too, when they said each of the six measures of barley represented a distinguished offspring of Ruth.
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