Learning Torah lishmah sweetens its fire into chesed

בענין מגילת רות בשבועות שהיא מצות גמילת חסדים י"ל על פי מ"ש בסוכה [מ"ט ב'] ותורת חסד על לשונה וכי יש תורה שאינה של חסד אלא הלומד תורה לשמה זו תורה של חסד ע"ש.

Concerning Megillas Rus on Shavuos, which is the mitzvah of gemilus chasadim (acts of kindness), one may explain it based on what is said in Sukkah [49b]: "and the Torah of chesed is on her tongue" (Mishlei 31:26) — is there then a Torah that is not of chesed? Rather, one who learns Torah lishmah (for its own sake) — this is Torah of chesed.

Megillas Rus, the story of kindness, is read on Shavuos. The Gemara asks why the verse specifies "Torah of chesed," since all Torah is good; it answers that Torah learned lishmah, purely for Hashem's sake, is uniquely called "Torah of chesed."

והענין הוא כי באמת התורה נקראת אש דת.

The matter is that in truth the Torah is called "eish das" (a fiery law) (Devarim 33:2).

The Torah in its essence is like fire — exacting and consuming, a "law of fire."

אך בפיהן של ישראל היא מתמתקת כמ"ש במד' כתפוח כו'.

But in the mouths of Yisrael it becomes sweetened, as the Midrash says on "like an apple tree…" (Shir HaShirim 2:3).

When Bnei Yisrael learn Torah, its fiery severity is transformed into sweetness, like the sweet fruit of the apple tree.

ופריו מתוק לחכי לחכי הי' מתוק כו'.

"And its fruit was sweet to my palate" — to my palate it was sweet…

The Torah, received and savored by Yisrael, becomes sweet to the one who tastes it.

והיינו מטעם שכתב שם במד' שתפוח אין לו צל וכולם ברחו רק בנ"י נמשכו לקבל התורה לשמה הגם שלא הרגישו שיהי' להם טובה לכן זכו למתיקות של התורה.

And this is for the reason written there in the Midrash, that the apple tree has no shade, and everyone fled from it, but only Bnei Yisrael were drawn to receive the Torah lishmah — even though they did not perceive that any benefit would come to them — therefore they merited the sweetness of the Torah.

The Midrash likens Torah to an apple tree, which offers little shade so people flee its discomfort. Other nations turned away, but Bnei Yisrael came forward to accept the Torah purely lishmah, with no thought of gain. Precisely because their acceptance was selfless — an act of chesed toward Hashem — they were rewarded with the Torah's sweetness.

וזהו השבח של בנ"י שתורת חסד על לשונה שבפיהן של ישראל שלומדין לשמה זוכין להפיק רצון ולמתק הדברים להיות תורת חסד [וזהו טעם מנהג ישראל לאכול חלב בשבועות]:

And this is the praise of Bnei Yisrael, that "the Torah of chesed is on her tongue" — for in the mouths of Yisrael, who learn lishmah, they merit to bring forth favor (ratzon) and to sweeten the words, so that it becomes a Torah of chesed. [And this is the reason for the custom of Yisrael to eat dairy on Shavuos.]

Learning lishmah turns the fiery Torah into a Torah of chesed — sweet and kind. The Sefas Emes hints that the minhag to eat dairy (sweet, milky foods) on Shavuos expresses this very theme: the once-fiery Torah has become sweet and nourishing like milk in the mouths of Yisrael.

Summary: Rus, the story of chesed, is read on Shavuos because Torah learned lishmah is itself a "Torah of chesed." The Torah in essence is "eish das," a law of fire, but when Bnei Yisrael — who alone came to receive it selflessly, expecting no benefit — learn it lishmah, its severity is sweetened into kindness, hinted by the custom of eating sweet dairy foods on Shavuos.