I shall find you outside
Song of Songs 8:1
In the weeks preceding the festival of Shavuot, it is customary to study the 39th tractate of the Mishnah, Ethics of the Fathers. The Ethics deals with the moral, rather than legal, dimension of Torah: while the other tractates outline the permissible and the forbidden under Torah law, the Ethics describes the spirit in which the Torah is to be approached, studied, and implemented, and the character and mindset that the Torah should inspire. Every year, as we approach the day on which we received the Torah from G-d at Mount Sinai, we study the Ethics in preparation for our annual re-experience of that event.
There are six Shabbatot between Passover and Shavuot, and on each of these Shabbat afternoons we study another of the Ethics’ six chapters. Actually, as it originally appears in the Mishnah, the Ethics contains only five chapters; a sixth chapter, The Acquisition of Torah, is taken from the Baraita (“external” talmudic literature) and appended to the Ethics for study on the Shabbat before Shavuot. As a result, this chapter has come to be regarded as the “sixth chapter” of the Ethics.
On the surface, this seems one of those accidents of history that determine the prominence or obscurity of a work: a gap in the calendar, the search for the appropriate “filler,” and the Ethics gains a chapter. But as our sages repeatedly point out, nothing in Torah is by chance or fluke. In the words of the famed Gaon of Rogachov, “Everything, even a thing that seems determined by force of circumstance, is purposefully directed and dictated by G-d.” Indeed, the story of the sixth chapter of the Ethics expresses a truth that is fundamental to the Torah, and to the significance of Shavuot in particular.
The Mishnah was edited by Rabbi Judah HaNassi (circa 200 CE), who sifted through thousands of teachings by dozens of sages over seven generations to compile a concise codex of Torah law. All subsequent discussion of Torah law is predicated upon the Mishnah; it forms the heart of the Talmud (which records three hundred years of exposition on the Mishnah) and is its ultimate point of reference. The teachings that Rabbi Judah did not include in the Mishnah are called Baraitot, from the word bara, “outside.” The Baraitot are widely cited by the Talmud to aid in the interpretation of the Mishnah or to support or refute a point of view, yet they are considered of a lesser status and authority than the Mishnah proper. Thus, the fact that a chapter of Baraita is “brought indoors” and elevated to inclusion in the Mishnah constitutes a quantum leap in its stature and significance.
Shavuot, as we said, is the day on which we “received” the Torah. But when our ancestors gathered at the foot of Mount Sinai on the sixth day of Sivan in the year 2448 from creation (1313 BCE), the Torah had already been in their possession for many generations. Abraham, Isaac, Jacob and Joseph all studied the Torah, as did the tribe of Levi in Egypt. Sinai marks not the disclosure of a hitherto unknown document, but the granting of a mandate that radically transformed the nature and import of this document. The Midrash offers the following parable to explain what happened on that first Shavuot:
Once there was a king who decreed: “The people of Rome are forbidden to journey to Syria, and the people of Syria are forbidden to journey to Rome.” Likewise, when G-d created the world He decreed and said: “The heavens belong to G-d, and the earth is given to man.” But when He wished to give the Torah to Israel, He rescinded His original decree, and declared: “The lower realms may ascend to the higher realms, and the higher realms may descend to the lower realms. And I, Myself, will begin”—as it is written, “And G-d descended on Mount Sinai,”  and then it says, “And to Moses He said: Go up to G-d.” 
Before Sinai, there existed a “decree”  that split reality into two wholly self-contained realms: the spiritual and the material, the G-dly and the mundane. Torah, the divine wisdom and will, could have no real effect upon the physical world. It was a wholly spiritual manifesto, pertaining to the soul of man and to the spiritual reality of the “heavens.” While its concepts could, and were, applied to physical life, physical life could not be elevated—it could be improved and perfected to the limits of its potential, but it could not transcend its inherent limitations and subjectivity. Nor could the spiritual be truly brought down to earth—its very nature defied actualization.
Then G-d dissolved the dichotomy He decreed at creation. A fissure was opened in the inviolable wall, a window from the inner world of the spirit to the external world of the material. The Torah could now sanctify physical life. The G-dly could now be made real, and the tactile made spiritual.
No longer did the old rules apply, where what was inside was locked in and what was outside shut out. Torah was empowered to extend beyond its spiritual parameters to embrace the dark, cold world of matter and imbue it with warmth and light.
Based on an address by the Rebbe, Shabbat Parshat Bamidbar 5749 (May 19, 1989)
. Many communities observe the custom of repeating the study of the Ethics after Shavuot, in the Shabbat afternoons of the summer months (until Rosh Hashanah).
. Rabbi Joseph Rosen, 1858-1936.
. Tzafnat Paane’ach on Numbers 33. According to the doctrine of hashgachah pratit (“specific divine providence”) taught by Rabbi Israel Baal Shem Tov, this is true of every event and phenomenon in G-d’s world; but it is even more emphatically so in everything that pertains to the Torah, which is G-d’s revelation of His wisdom to man.
. Rashi on Genesis 26:5 and 46:28; Pirkei d’Rabbi Eliezer 8:1; Talmud, Yoma 28b and Kiddushin 82a; Chizkuni on Exodus 5:4.
. Psalms 115:16.
. Exodus 19:20.
. Ibid., 24:19.
. Midrash Tanchuma, Va’eira 15.
. In Hebrew, the word gezeirah means both “decree” and “split.”
. Sefer Hasichot 5749, pp. 480-486.