It is only appropriate that the Torah, which brings peace and harmony to the entire world, was given on the Day of Rest.
The Rebbe explains:
– Shabbat is intrinsically connected with the holiday of Shavuot as reflected in our Sages’ statement:
“… Everyone agrees that the Torah was given on Shabbat” (Shabbat, 86b).
Shabbat is characterized by the quality of rest as our Sages commented:
“What was the world lacking? Rest. When the Shabbat came, rest came” (see Rashi’s commentary on “Breisheet”, 2:2).
Similarly, when reciting the Blessing after Meal on Shabbat, we add:
“May the Merciful One let us inherit the day which will be all Shabbat and rest for eternal life.”
And in our Minchah prayers we speak of “a day of rest… a rest of peace… a perfect rest with which You find favor.”
This dimension of rest was brought to a complete state by the giving of the Torah. Our Sages relate, the world was in a state of uneasiness until the giving of the Torah, and only when the Torah was given, did it reach a state of tranquility (see Avodah Zarah, 3a). Thus, the concepts of rest and tranquility represent an intrinsic connection between Shabbat and the giving of the Torah.
To explain this concept in depth:
The natural state of the world is one of change and activity, the very opposite of rest. Indeed, the very concept of time, the fundamental framework in which the entire creation operates, is characterized by change. Shabbat, in contrast, brings about rest and unity, revealing the fundamental G‑dly oneness that lies at the core of the entire creation. Thus, Shabbat takes us above the entire framework of time and therefore on Sunday, we say “This is the first day of the week,” since the cycle of time starts anew.
In a full sense, this rest and oneness was introduced by the giving of the Torah. For it is through the Torah, that the purpose for the entire creation can be realized.
This concept can be understood through a parallel to our personal state. When a person does not realize the purpose for his existence — which is “to serve His Creator” — he can never experience true tranquility and calm. On the contrary, the changes and multiplicity in the world at large disrupt and disturb him. When, however, a person is aware of the purpose for his existence and for each aspect of his life, he rises above all this treadmill of activity. This, in turn, allows a person to reach a state of fulfillment and development.
Furthermore, the awareness of one’s purpose generates tranquility, not only for the person himself, but for the activities which he carries out in the world. This allows them to be carried out with added perfection and success; and thus spreads rest and tranquility throughout the world.
Similarly, in regard to the giving of the Torah: When the Jews received the Torah, the purpose of the entire creation — that it was brought into being for the sake of the Torah and for the sake of the Jewish people — was revealed. When the Jews observe the Torah and its mitzvos, and influence the gentiles to observe their seven mitzvos, they transform the world into a dwelling for G‑d, and in this way, spread rest and tranquility throughout the world, encompassing every particular dimension of existence.
Based on the Rebbe’s talk on Shabbat Parshat Bamidbar and Motzaei Shavuot, 5751. Free translation.