The mitzva of Shabbat appears in the Ten Commandments. These appear twice in the Torah, once in the book of Exodus and once in the book of Deuteronomy. In each version a different reason is presented for the mitzva of Shabbat. Rambam discusses these two reasons and asserts that they reflect two aspects of Shabbat: First, it is a day when people rest from their labors, and this strengthens faith in the Creator, who created the world in six days and rested on the seventh day. Second, the mitzva to keep Shabbat was given to us because we were slaves in Egypt and were unable to rest when we wished to, and the cessation of labor reminds us that the Creator brought us out of Egypt.

Resting strengthens our awareness of Creation:

You know already from what I have said that opinions that are not confirmed, established, and made permanent in public by [the performance of] actions do not persist. Therefore, He commanded us to honor this day, in order to confirm thereby the principle of Creation which will spread in the world, when all people will rest on one day [each week]. When people ask: “Why is this is done?” The answer will be: “Because in six days the Lord made [the heavens and the earth…]” (Exodus 20:11).

The different reasons given for Shabbat in the two versions of the Ten Commandments express two different aspects of the day:

Two different reasons are given for this mitzva, because of two different objectives. The first version of the Ten Commandments gives the reason for honoring Shabbat as it says: “Because in six days the Lord made [the heavens and the earth, the sea and everything that is in them, and He rested on the seventh day; therefore, the Lord blessed the Sabbath day and sanctified it]” (Exodus 20:11). In the book of Deuteronomy it says: “You shall remember that you were a slave in the land of Egypt, [and the Lord your God took you out from there with a mighty hand and with an outstretched arm]; therefore, the Lord your God commanded you [to observe the Sabbath day]” (Deuteronomy 5:15).

The first reason relates to Shabbat as a day that strengthens belief in Creation. The second reason concerns the need to remember that we were slaves in Egypt and that God redeemed us:

This difference can easily be explained. In the former, the reason given is the sanctification of the day and its honor: “Therefore the Lord blessed the Sabbath day and He sanctified it” (Exodus 20:11), and the reason for this is “Because in six days….” But the fact that God gave us the laws of Shabbat and commanded us to keep it is the consequence of our having been slaves; for then we did not work by choice, nor at the time we wished to; and we could not rest.

Shabbat is meant to increase awareness of these two fundamental concepts:

Therefore, God commanded us to abstain from labor and to rest so that we should combine the two purposes: (1) That we believe the true principle, that the world was created ex nihilo, which clearly leads to the principle of the existence of God. (2) That we might remember how kind God was in freeing us from the burden of the Egyptians. Shabbat is therefore a double blessing: it gives us correct notions, and also promotes the well-being of our bodies. (Rambam, Guide of the Perplexed II:31)

Further reading: For more on Shabbat, see A Concise Guide to the Torah, pp. 174, 192, 226; A Concise Guide to the Sages, p. 275; A Concise Guide to Halakha, p. 379. For more on the difference between the two renditions of the Ten Commandments, see A Concise Guide to the Sages, p. 277.