The Torah portion of Sisa contains an entire section1 relating to Shabbos. It begins by stating that Shabbos is “a sign between Me and you for all generations, so that you know that I, G‑d, am making you holy.” The section concludes: “And the children of Israel shall observe the Shabbos … as an everlasting covenant … for in six days G‑d made heaven and earth, and on the seventh day He ceased working and rested.”

Why is Shabbos and its laws discussed here at such length, when it was already covered in detail2 as part of the Ten Commandments?

Our Sages derive3 from the words “He ceased working and rested,” that “An additional [measure of] soul is granted [the Jew] on the arrival of Shabbos. With the departure of Shabbos, it departs as well.” Moreover, our Rabbis explain4 that spices are sniffed on Saturday night during the Havdalah service so as to becalm the person’s soul, which is perturbed by the departure of the additional soul.

The Alter Rebbe thus writes in his Shulchan Aruch :5 “The Sages have established that spices be sniffed every Saturday night in order to pacify the soul. For it laments the departure of Shabbos because of the additional soul that has departed. Therefore it is assuaged and gladdened with a pleasant odor.”

What exactly is meant by the statement that “an additional [measure of] soul is granted [the Jew] on the arrival of Shabbos”?

According to the Zohar, this literally refers to an additional measure of spirituality that is granted from above as a gift on Shabbos. The esoteric portion of Torah, however, explains it differently.

Rashi6 says that it means that a person is given the ability to savor Shabbos in a state of tranquillity; he is able to eat and drink and enjoy Shabbos unhindered by the worries of the weekday. The Rashba7 says: “There are those who explain that the additional soul refers to the tranquillity and delight that the soul finds on Shabbos, so that it is as if the person is granted an additional soul.”

Thus, according to the revealed portion of Torah, the additional soul does not refer to an additional measure of spirituality, but rather to a state of mind that enables and also results from the tranquillity and delight of Shabbos.

Why then is this termed “an additional soul,” rather than simply “a state of mind” or “a state of tranquillity” and the like? Because this tranquillity and delight of Shabbos is so pronounced that it effects an actual change in the person; it is as if the individual gains an additional soul.

This is to be understood as well from the fact that our Sages derive this understanding of the additional soul specifically from the verses in our Torah portion, and not from any earlier passage.

There is a novel aspect to Shabbos as described in Sisa. Previously, the Torah emphasized that Shabbos is markedly different from weekdays — “For in six days G‑d made heaven and earth … and rested on the seventh day. Therefore G‑d blessed the day of Shabbos and hallowed it.” Here, however, the verse states that Shabbos is “a sign between Me and you … that I, G‑d, am making you holy,” and that Shabbos is “an everlasting covenant.”

In other words, the Ten Commandments speaks of Shabbos in and of itself. Our portion addresses the effect that Shabbos has on the Jewish people.

This is particularly apparent in light of Rashi’ s comment on the verse “it is a sign between Me and you”: “It is a great symbol between us that I have chosen you, in that I have given you My day of rest for rest.”

Rashi is in effect telling us that the Jews’ rest on Shabbos involves more than merely relaxing and resting from labor, but that it is G‑d’s day of rest. As a result, repose on this day effects an elevation within the Jew himself.

This is also emphasized by Rashi when he explains “a Shabbos of Sabbaths” to mean: “a repose of stillness and not a temporary rest.” In other words, a Jews’ rest on Shabbos entails a complete change in his being. This type of Shabbos tranquillity and peace can truly be termed an additional soul — G‑d’s tranquillity and quietude that is granted on Shabbos to and within each Jew.

Based on Likkutei Sichos , Vol. XXXI, pp. 191-195.