As part of the Ten Commandments, Exodus 20:8-11 states the text of the fourth commandment, the Sabbath.

Remember the Sabbath day and keep it holy. Six days you shall labor and do all your work, but the seventh day is a Sabbath of the L-RD your god: you shall not do any work- you, your son or daughter, your male or female slave, or your cattle, or your stranger who is within your settlements. For in six days the L-RD made heaven and earth and sea, and all that is in them, and He rested on the seventh day; therefore the L-RD blessed the Sabbath day and hallowed it.

As is well known, the exposition of the Ten Commandments in Deuteronomy presents a different reason for the Shabbat.

Observe the Sabbath day and keep it holy, as the L-RD your God has commanded you (Deut. 5:12)…Remember that you were a slave in the land of Egypt and the L-RD your God freed you from there with a mighty hand and an outstretched arm; therefore the L-RD your God has commanded you to observe the Sabbath day. (Deut. 5:15)

Which reason is primary: the one given in Exodus that begins with Remember [Zakhor], or the other given in Deuteronomy that begins with Observe [Shamor]? Moreover, why does the Torah present both the Exodus reason- creation of the universe by God, and the Deuteronomy reason- deliverance of the children of Israel from Egyptian bondage? Finally, what is the relationship between the two reasons? Rambam devotes an entire chapter of The Guide of the Perplexed to these topics (Guide 2:31, Pines ed., pp. 359-60). His explanation emphasizes themes that are present throughout his presentation in the Guide of ta‘amei ha-mitzvoth. He emphasizes correct opinions, he emphasizes that actions are commanded to inculcate correct opinions, and he insists on the teleological benefits that the mitzvah has for those who are commanded to observe it- in this case, both a physical and intellectual/spiritual benefit.

He writes as follows:

Perhaps it has already become clear to you what the cause of the Law’s establishing the Sabbath so firmly and ordaining death by stoning for breaking it is. The Master of the Prophets has put people to death because of it. It comes third after the existence of the Deity and the denial of dualism. For the prohibition of the worship of anything except Him only aims at the affirmation of the belief in His unity. You know from what I have said that opinions do not last unless they are accompanied by actions that strengthen them, make them generally known, and perpetuate them among the multitude. For this reason we are ordered by the Law to exalt this day, in order that the principle of the creation of the world in time be established and universally known in the world through the fact that all people refrain from working on one and the same day. If it is asked: What is the cause of this? The answer is For in six days the L-RD made…[Exod. 20:11].

For this commandment two different causes are given, corresponding to two different effects. In the first Decalogue [Exodus], the cause for exalting the Sabbath is stated as follows: For in six days the L-RD made and so on. In Deuteronomy, on the other hand, it is said: Remember that you were a slave in the land of Egypt…; therefore the L-RD your God has commanded you to observe the Sabbath day [Deuteronomy 5:15)]. This is correct. For the effect, according to the first statement [in Exodus], is to regard that day as noble and exalted. As it says:  therefore the L-RD blessed the Sabbath day and hallowed it [Exod. 20:11].This is the effect consequent upon the cause stated in the words: For in six days, and so on. However, the order given us by the Law with regard to it and the commandment ordaining us in particular to keep it [i.e., the verse in Deuteronomy] are an effect consequent upon the cause that we had been slaves in Egypt where we did not work according to our free choice and when we wished and where we had not the power to refrain from working. Therefore, we have been commanded inactivity and rest so that we should conjoin the two things: the belief in a true opinion- namely, the creation of the world in time, which, at the first go and with the slightest of speculations, shows us that the Deity exits- and the memory of the benefit God bestowed upon us by giving us rest from under the burden of the Egyptians (Exod. 6:7). Accordingly, the Sabbath is, as it were, of universal benefit, both with reference to a true speculative opinion and to the well-being of the state of the body.

In Guide 3:43 (Pines ed., p. 570), Rambam reiterates these ideas.

With regard to the Sabbath, the reason for it is too well known to have need of being explained, for it is known how great a test it procures. Because of it, the seventh part of the life of every individual consists in pleasure and repose from the fatigue and weariness from which there is no escape either for the young or for the old. At the same time, it perpetuates throughout the periods of time an opinion whose value is very great, namely, the assertion that the world has been produced in time.

Elsewhere, (Guide 3:31), Rambam emphasizes that “every commandment from among these the six hundred and thirteen commandments exists either with a view to communicating a correct opinion, or putting an end to an unhealthy opinion, or to communicating a rule of justice, or to warding off an injustice, or to endowing men with a noble moral quality, or to warning them against an evil moral quality. Thus, all [the commandments] are bound up with three things: opinions, moral qualities, and political civic actions” (Pines ed., p. 524). In the case of Shabbat, the Rambam’s interpretation of the dual declarations of Zakhor and Shamor, combined with the two reasons of the creation of the universe by God and the release from the bondage of Egypt yield a result that one commandment contains with itself benefits both “with reference to a true speculative opinion and to the well-being of the state of the body.”