Shavuos - holiday of Torah she'baal peh

Sefas Emes (5633):

ענין קריאת רות בשבועות. שהוא ענין תורה שבע"פ

How is Rus about Torah shebaal peh, and if that is indeed the takeaway from the  book, why do we read it on Shavuos, which at first glance is a celebration of the written Torah, a celebration of receiving luchos which were engraved and written by G-d?

My wife wrote on her blog:

This year, I was thinking about parallels between Megillat Esther and Megillat Ruth. In both, the heroine for whom the book is named has a parental figures who is not her actual parent as a guide. This figure advises her about how to behave in a new environment for her -- Mordechai directs Esther to remain silent about her identity, and Naomi instructs Ruth about halachos and social norms in Jewish society in general and told to stick with the maids working in Boaz's field

Subsequently, though, that same authority figure turns the tables on the heroine due to what has come to light to change her tactics and take a great risk. The heroine then has to act contrary to her nature and take action that would be considered rash and dangerous. She must subjugates her own views to that of the wisdom of the parental figure.

She refers to Mordechai's instruction to Esther to go to Achashveirosh even uninvited in order to thwart Haman's plot, and Naomi's instruction to Rus to go to Boaz and meet him in the field in the middle of the night, seemingly unsuitable behavior for a bas yisrael. My wife ends off:

Interestingly, both heroines thus prove themselves worth of royalty, for the middah of malchus in Jewish thought is not of self-assertion but of receiving. I'd venture to say that Esther (descended from the line of Rachel) may represent the role of Moshiach ben Yosef while Ruth clearly establishes the line leading to David and the Moshiach born of that dynasty.

How does Rus express her commitment to Judaism?   She doesn't pull out a kitzur shulchan aruch, or some other guidebook that tells her how to behave and pledge to follow it.  She tells Naomi, "Ba'asher teileichi eilech, ba'asher taluni alin" -- "Where you go, I go," etc.  It is Naomi's behavior and practice that is her guide.  It is Naomi's instruction that she follows, irrespective of the risk to her reputation, or in Esther's case, to her life. 

These heroines prove worthy of the midah of malchus because "man malchi -- Rabbanan."   Without a concept of mesorah, without Rabbinic interpretation, without role models and tradition, Torah could not endure.  It is the mesorah, the Rabbis, who rule over the text, not the text which rules over the mesorah. 

Even though the Torah says an Amoni may not intermarry into Klal Yisrael, Boaz came along and revealed that an Amonis is excluded from that law.  Boaz = Bo Oz, the Torah was embodied within him, his interpretation and mesorah defined what the rules of the game were.  

That's why the parallel to Rus is the story of Esther, which we read on Purim.  "Hadar kiblu'ha b'ymei Achashveirosh..."  Purim is also a celebration of kabbalas haTorah, and therefore, this same theme of a living, breathing mesorah is a focal point of the megillah story.

The tachlis of mattan Torah, what we celebrate on Shavuos, can be summed up in three words: Lo BaShamayim Hi.  Mattan Torah is in fact all about Torah shebaal peh because at that moment of mattan Torah G-d turned over the reins to us and Torah became more than just words on a page.