God gave all humanity only Seven Laws: seven and not eight. If someone states, for example, that one must keep the Sabbath, he is not only wrong but he is violating Torah, as this would involve transgressing the overarching Torah prohibition, implicit in the Seven Laws, against Noahides making a new religion for themselves. Therefore, again, Seven and not Eight.
However, having stated the halacha [the Torah law] concerning the matter, there are prominent rabbis that have commented on the idea of the non-Jewish world, observant Noahides, remembering and observing the Sabbath in some way, although not in the exact same way as the People of Israel, the Jews
Rambam, Rabbi Moshe ben Maimon (Maimonides), in his eye-opening work The Guide of the Perplexed, asks how we can understand the reason for the severity of the penalty of an Israelite violating the Sabbath. He then states that commandment of the Sabbath, “is the third from the commandment concerning the existence and unity of God.” He then continues to explain the reasons this day, the Sabbath, is to be given honor.
Two Different Reasons: Two Different Objectives:
Two Different Reasons
1). In the Decalogue in Exodus, the Torah, the reason for distinguishing the Sabbath is “For in six days…”
2). Also, in the Decalogue, Deuteronomy, the Torah, “And thou shalt remember that thou hast been a slave in the land of Egypt….., therefore the LORD (Hashem) thy God has commanded thee…”
Two Different Objectives
Rambam states that two different reasons can easily be explained.
1). The first reasons objective is to bring honor and distinction by informing us that, “Therefore the LORD (Hashem) hath blessed the day of the Sabbath and sanctified it….” and the cause is , “For in six days…”
2). The second reasons objective is to remind Israel of a time when they were slaves and had no control over when they would work or not.
This leads us to: Two Purposes for Israel to abstain from work on the Sabbath.
1). That we might confirm the true theory, that of Creation, which at once leads to the theory of the existence of God.
2). That we might remember how kind God has been in freeing us, (Israel) from the burden of the Egyptians.
He reminds us that indeed the Sabbath is a double blessing: 1). It gives us correct notions, that is of God. 2). And according to Rambam, “promotes the well being of our bodies.”
Now, what we like to point out in this very short but very important section is his words that preceded all of the above and as to why he would speak such words?
He writes: “Therefore, we are told in the Law, Torah, to honor this day, in order to confirm the principle of Creation which will spread when all peoples [emphasis added] keep the Sabbath on the same day.”
We propose that it is the first reason - the primary objective - of the Sabbath, regarding Creation ex nihilo, that's the primary basis of this statement It is important, or let us say imperative, that all of humanity acquires true and correct conceptions of the Creator. It is this day, the Sabbath, that provides us with the true conception of the existence and unity of God, which should be well-known to all humanity. Even the Biblical prophets speak of this in very clear terms in many different ways. “In that day the LORD (HaShem) will be One and His Name will be One." Of course HaShem is already One, but His Name is not yet confirmed or even known by all of humanity. But, the prophets promise, the time is coming when all of humanity will indeed know His holy Name
Since it is one of the two key objectives of this day, the Sabbath, to provide proof of the existence and unity of God, we have to ask this question: Should the great majority of the human race allow this great and holy day to just pass by as any other day? Or, should not all humanity - as we will indeed do one day, according to both the prophets and Rambam - treat this day with honor and respect? In this connection, we think we must be mindful of Rambam’s words, “ to honor this day, in order to confirm the principle of Creation which will spread when all peoples keep the Sabbath ON THE SAME DAY.” [Emphasis added]
Another notable individual, much more recently, speaks to this same point. He is Rabbi Umberto Moshe David Cassuto. He served as the chief rabbi of Florence, Italy from 1914-1925. Later, fleeing Mussolini's fascism, he would later move to Israel. He became a professor at Hebrew University in Jerusalem.
In his book, The Documentary Hypothesis, Lecture 3, More About the Divine Names, he alludes to the possibility of the reason for the use of different Divine names in the Creation story.
He writes that, in the last section of the Creation story in the Bible, which speaks of the Sabbath, one would expect to find the four-letter Name of HaShem, the Tetragrammaton. But that's not the Name the Bible uses. As he says “… the last paragraph of the section speaks of the Sabbath, which is a precept exclusive to Israel, and therefore the Israelite name of God was [supposedly] required. To this one may reply that, on the contrary, it was the special intention of the Torah here to teach us that the sanctity of the Sabbath flows from cosmic reasons, and antedates Israel, and rests on the world as a whole.
"Although the commandments appertaining to the manner of observing the Sabbath, which were subsequently prescribed in the Torah, are incumbent only on Israel, yet the Sabbath per se [as such] was hallowed from the time that the world came into being, and its sanctity is not something restricted to the people of Israel.” He goes on to say that the confirmation of his view is to be found in these words of Scripture, where Israel was told, “Remember [emphasis added] the Sabbath day, to keep it holy." God did not tell Israel to know that there is such a thing as the Sabbath in the world, He only wants Israel to recall it. From this the rabbi concludes that the idea of the Sabbath is not something new to humanity, and that the idea of the Sabbath was already common knowledge.
So, obviously, both rabbis agree that the Sabbath somehow, in some way, involves all of humanity. According to Rambam, a true conception of the Creator, blessed be His Name, as well as Creation itself, will not be realized until all peoples everywhere keep the Sabbath on the same day. Rabbi Cassuto's sense is that the Sabbath-day applies to the whole world; the Torah's precise instructions for observing it govern Israel alone; but the sanctity of the Sabbath is, definitely, not something that is restricted to the people of Israel only.
So, while Sabbath-observance is not one the Seven Mitzvot, the Seven Noahide Laws, we believe that there is, definitely, some manner of obligation or duty for all humanity to remember this day and the truths that it teaches. Since these truths are not meant to be limited just to Israel, for Israel to have a strict monopoly on them. Rather, they are all-important universal truths. Surely, then, they are and should be known by all the world - by all humanity.
Rabbi Bachya ben Joseph ibn Paquda, an 11th-century sage, states, in his extraordinary work, Duties of the Heart, that a person's obligation of service [to God, of Divine service] directly corresponds to the degree of favor that has been bestowed upon him or her. He states that people come under an obligation of increased service according to the favor, in general, or community-wide, and in particular, or individually, bestowed by God. He continues by saying that favor from God is bestowed in four different ways.
The first kind of favor, he states, is “the goodness of the Creator which embraces all of mankind: He brought them into existence when previously they did not exist; He gives them life; He favors them with all that we have spoken of [in another section]. They are accordingly under a universal obligation [emphasis added] of service of the Creator, may He be exalted. This consists of [obedience to] all the commandments called for by the intellect [that is, the Seven Noahide Laws], which were observed by Adam, Hanoch, No’ach and his sons, and Iyov [Job] and his friends, up to the days of Moshe [Moses], our Master, peace be upon him."
"Whoever adheres to all these for the sake of God’s service, God will bestow upon him favors beyond those enjoyed by other people, and will raise him to a higher level in this world and give him great reward in the world-to-come, as with Avraham, to whom God said, “Do not fear, Avram: I am a shield to you; your reward will be very great” (Bereshis [Genesis] 15:1)
Now, personally speaking, I understand the only reason for my existence and my continued existence on this earth is the Divine favor and kindness of God. If so, I believe, then I personally, necessarily, have the great obligation, privilege, and honor to do God's will: to serve God as His servant.
Having this obligation, and understanding the extremely universalistic idea that the Sabbath day conveys, that is, the existence and unity of the Creator, how can I allow the Sabbath to come and go without me recognizing it in some way?
If I understand Rambam in Guide for the Perplexed correctly, the great truths of God’s existence and His unity will not be fully recognized until all the peoples of the world observe the Sabbath. So wouldn't I be found to be a fool or an ingrate, or both, if I allowed it to go by without at least reflecting on it? Wouldn't that be a kind of fighting against God, and thwarting His purpose for the day?
May the day come, speedily in our time, when all people observe the Sabbath with Israel. Then the whole world will recognize His existence and unity, and then it shall be as the prophet declared, “In that day the LORD will be One and His name will be One.”
 The Guide for the Perplexed, Dover Publications, Inc., New York, Book II, Chapter XXXI, 1956. pp. 218-219
 The Documentary Hypothesis, Shalem Press, Jerusalem and New York, 2006, pp. 38-39
 Duties of the Heart, Feldheim Publishers, Jerusalem & New York, Vol. 1, The Gate of Serving God, Chapter 6, pp. 303-305
 Guide for the Perplexed, ibid.