The 7th day: The End for Mankind
In a recent shiur, a Rabbi quoted Nachmanides (Ramban) on Leviticus 25:2. This verse refers to the law concerning our rest from working the land; the Sabbatical Year. The Torah verse says this year must be a "Sabbath unto God". Nachmanides teaches that this term "Sabbath unto God" appears only twice in Torah: once here, and once in Exodus 20:10 (in the Ten Commandments) addressing the seventh day. Both the Sabbath, and the seventh, Sabbatical Year share the same design, and by the words "Sabbath unto God", a similar objective. Why must years duplicate the first seven days?
Later in his commentary, Nachmanides says these words: "Behold, the days allude to to that which was created in the act of Creation; and the years allude to that which will be in the creation of all the days of the world." He means to say that the days – working six days and resting on the seventh – remind us of God's act of Creation. The past. We require a weekly reminder of this fundamental, that all exists only due to God alone. But what does Nachmanides mean by "the years allude that which will be in the creation of all the days of the world"? I believe Nachmanides is teaching us an amazing idea.
When God created the world in six days, our focus tends to remain on those days, and not the seventh. This is because the universe is magnificent, replete with marvels at every turn. We focus on physical objects and laws that captivate our thoughts. But when reading Genesis 2:2, we wonder at the apparent duplication: "And God completed His work that He did on the seventh day; and He rested on the seventh day from all the work that He performed." The question is glaring: if it already states that God "completed" His work, how can he do another act of "resting"? He is already at rest! the answer is as follows.
Suppose I am drinking a soda, and then I place the cup down and stop drinking. There are one of two reasons why I stop drinking: 1) no soda remains; or 2) I commence a diet at that moment. I the latter case, my abstention form drinking is due to a "positive" act of dieting in which I now engage. My inactivity is not a passive act, but a positive commitment to some ideal.
When God "completed" Creation, it was due to the fact that all that He wished to exist, now existed. Nothing was left to create. But when God "rested", He gave rest a "positive" designation. God was designating Sabbath as the objective of creation, not merely a day with nothing to do since all was created. The Licha Dodi recited Friday night says, "The last in creation, but first in His thought". Although Sabbath came after all else was formed, it was first in God's thought. Meaning, it was the purpose of Creation. What is the purpose of Sabbath?
Sabbath is a day when man cannot engage in creative labor. He is freed from all physical preoccupation in Earthly establishment (issur melacha), he is commanded to partake in physical pleasures (oneg Shabbat), but mostly, he is to immerse himself in Torah and all thoughts about God's creation. This is what the refrain from the physical targets as its objective.
The universe is truly a laboratory for man to witness and experiment with God's creation, for the purpose of arriving at new observations and learning God's wisdom as far as humanly possible. Therefore, Sabbath is the choicest of days, since God desired man to engage a life of wisdom, over a life of physical toil.
Why then wasn't Adam commanded in the Sabbath? This is because Adam was not yet sentenced to work for his needs. (Gen. 3:17) Adam had all his needs prepared. He enjoyed that preferred state where he could devote all his energies to wisdom. He lived a truly "Sabbatical" existence. A command of Sabbath would have produced no change in his activities. But once sentenced to labor after the sin, Sabbath entered the picture when Torah was given. But the Sabbath is not to remain eternally as a "weekly" event...
Messianic Times: the Final Sabbatical Era
The Rabbis refer to the Messianic era as a time that is "entirely Sabbath". In the future, man will once again enjoy the state where he works minimally, and engages the pursuit of wisdom as his main focus. In other words, and here's Nachmanides' point: the original Sabbath was a model for man's ultimate state. Man was originally meant to be fully immersed in a life of wisdom and this is why man alone received the gift of intelligence. Although we are temporarily distracted by the need to work, God will finally create a state where mankind will recognize Him, "v'kol bnei bassar, yikru b'shimecha", "And all sons of flesh will call in Your name". Sabbath is the choicest of days, as it is the state where man lives as originally planned: immersed in studying God. And this state will soon be an enduring state, not simply a weekly event. (Of course, the law of Sabbath remains, as the Torah will never change.)
Perhaps this is what Nachmanides means when he says, "the years allude to that which will be in the creation of all the days of the world". The years refers to the Sabbatical Year. By receiving this command to rest for an entire year, God teaches that man's state can in fact tolerate an elongated state of preoccupation with Torah, without physical toil. We don't need to labor to be happy. Just the opposite is true. The Sabbatical year points to the ability in man to enjoy thought on a prolonged basis. And then we have the Jubilee, where after a period of seven cycles of seven years, we again must rest the land. This time, two consecutive years of rest: the 49th and the 50th. We see an even longer period that carries the original design of Sabbath. This continually protracted approach – 6 days + 1 rest day; 6 years + 1 rest year; 7 x 7 years + 2 rest years – all point to the next span of time in this continually increasing pattern: the Mesianic Era, which will not end.
It is amazing that the first seven days serve the purpose of bringing creation into existence, but also allude to all the days of the world. We may rightfully say that the millennium from Adam until the Messiah are the "first six days" of mankind, and from the Messiah and onward is a "seventh day", a "day" of Sabbath, that lasts forever. The first seven days thereby foretell the entire history of mankind, based on the objective that man engage intelligence over all else. That is something.
Perhaps too this is one reason for Resurrection of the Dead; that all those who have passed will yet enjoy the preferred human state.
 "Sabbath unto God" means a timeframe where man is dedicated to knowledge of God, not a day that God needs. For God has no needs. All God's commands are for human benefit.