It took six days for God to create the heavens, the earth, and all within them. At first glance, an additional day seems unnecessary. Nevertheless, God created the seventh day and designated it for rest and cessation of labor. As a result, the world contains rest, blessing, and holiness. Thus we read:
The heaven and the earth were finished, and all their array. On the seventh day God finished the work that He had been doing, and He ceased on the seventh day from all the work that He had done. And God blessed the seventh day and declared it holy, because on it God ceased from all the work of creation that He had done. (Bereishit 2:1-3)
The Sages ask:
Does God really get tired? Is it not already stated: “The Lord is God from of old, Creator of the earth from end to end. He never grows faint or weary” (Yeshayahu 40:28)? Not only that, but He actually gives the weary strength, as it is written: “He gives strength to the weary” (ibid. 29). Why then does it say: “He rested on the seventh day” (Shemot 20:11)? It is as though God declared that He created His world in six days and rested on the seventh. (Mekhilta Yitro)
Why did God dictate that even He must rest on the seventh day? In order to create rest, satisfaction, tranquility, and calm for the world. As long as God was busy creating the world, the world was constantly expanding; when He rested on the seventh day, rest was given to the world (Bereishit Rabba 10:9).
Nonstop work, without rest, expresses a tremendous yearning for perfection and an unending sense of a void that can never be filled. Despite all of our work, toil, and travail, we are unable to achieve satisfaction and peace of mind, because perfection remains so far away, and our shortcomings extend indefinitely. There is so much emptiness to fill and so many problems to fix that we can never stop working. This is how people would be living if the world had been created in six days without Shabbat. But with the creation of Shabbat, the world was blessed with rest (Maharal, Tiferet Yisrael ch. 40).
One is able to rest when he knows that his actions are valuable. He derives satisfaction from his labor, knowing that his work is not for naught. This allows him to gather his strength and ready himself for the next stage, when he will resume working. However, if one does not appreciate the value of his work, he will not be blessed with peace of mind even if he stops working. This was true at the beginning of the world as well. Although the heaven and earth, continents and oceans, trees and grasses, luminaries and the deep, fish, birds, and animals were already created, and even though man – created in the divine image – already walked therein, the world was still devoid of meaning, and thus there was no rest. With the creation of the seventh day for rest and cessation of labor, the ability to absorb the inner worth of the world and all actions taken in it was created as well.
To a certain extent, all of mankind has internalized the idea that the creation of the seventh day gives meaning to work and creation, thus allowing everyone to enjoy rest and draw satisfaction from labor. To benefit from this it is not necessary to rest specifically on Shabbat. But the true and absolute value of creation and work, their divine aspect, can be internalized only by resting on Shabbat, the day that God designated for rest. This is a privilege granted to Israel alone. Furthermore, Jews cannot find rest through any finite human value: “Our place of rest is only through God” (R. Kook’s Orot, Zeronim, “Tzima’on Le-El Ĥai”).
Without that rest, which expresses the value and purpose of the world, there is no point in its existence. Thus the Sages state: “This can be compared to a king who built, sculpted, and decorated a marriage canopy. What was missing? A bride to enter it! Similarly, what was the world missing? Shabbat” (Bereishit Rabba 10:9). Of what use to the king are all the rooms in the palace and their beautiful furnishings if he does not have a bride to enjoy them with? The bride brings blessing to the palace, because the delight she provides for the king leads him to be benevolent toward the entire kingdom. The Sages further state (ibid.): “This can be compared to a king who made a signet ring for himself. What was lacking? The seal! Similarly, what was the world lacking? Shabbat.” The seal is what gives a signet ring meaning and identity. Similarly, Shabbat with its sanctity supplies meaning to the world (Maharal op. cit.).