Regarding the deep purpose of "sabbath" Wirzba explains this way:
Quoting from a midrash (interpretive elaboration of Torah), the medieval rabbi Rashi claimed that after the six days of divine work creation was not yet complete. What it lacked, and thus what remained to be created, was menuha, the rest, tranquility, serenity, and peace of God. In the biblically informed mind, menuha suggests the sort of happiness and harmony that come from things being as they ought to be; we hear in menuha resonances with the deep word shalom. It is this capacity for happiness and delight, rather than humanity, which sits as the crowning achievement of God's creative work. It is as though by creating menuha on the seventh day God gathered up all previous delight and gave it to creation as its indelible stamp. Menuha, not humanity, completes creation. God's rest or shabbat (sabbath), especially when understood within a menuha context, is not simply a cessation from activity but rather the lifting up and celebration of everything.
It's an important point to recognize that it was not God's intent to see the created world apart from the purposes of delighting in it. The secular and cultural sabbath which most people enjoy by having a "day off" from work each week does not capture the meaning of the biblical intent. While it gives us pleasure to have a day "to ourselves" for the enjoyment of recreation, extra sleep, and leisurely activities, it does not go so far as to promote our active participation in the restful, though active, reflection and delight in the created order, nor in the Creator.
This passage from Wirzba is an important elaboration upon the first one noted above:
The creation of menuha is not a divine afterthought. Nor should it be viewed in a passive way, as a mere withdrawal from exertion. God's rest on the seventh day did not amount to a pulling back but rather a deep sympathy, harmony, and celebration with all that was there. In so delighting in the splendor of creation, God invites creatures to bask in the glory of the divine life. In a most important way, therefore, the creation of menuha gave to the whole of creation its ultimate purpose and meaning. Without menuha creation, though beautiful, would be without an all-encompassing, eternal objective which is to participate in the life of God forever. And so what Sabbath menuha does is give us a positive vision in which there is no fear, distrust, or strife. There is rather a celebration of, and a sharing in, God's own experience of delight.
Sabbath, being the climax of creation, is thus the goal toward which all our living should move. It is not merely an interlude within life, but rather its animating heart, suffusing every moment with the potential for joy and peace. It is the interpretive key that helps us understand what all the moments and members of life mean. It gives aim and direction to life so that we know how and where we are to move. Life's fullness or happiness cannot be achieved in the absence of divine delight. It is what God wants for us and for all creation. Abraham Joshua Heschel put this point beautifully when he said, "All our life should be a pilgrimage to the seventh day; the thought and appreciation of what this day may bring to us should be ever present in our minds. For the Sabbath is the counterpoint to living; the melody sustained thoughout all agitations and vicissitudes which menace our conscience; our awareness of God's presence in the world." Insofar as we genuinely experience Sabbath menuha, we catch a glimpse of eternity, a taste of heaven.
So, it is incumbent on people, especially people of faith who regard their lives as a gift from God to Whom we owe our praise and obedience, to reflect upon the progress we are making toward the realization of Sabbath observation in our lives. To aid in our reflection, Wirzba offers this conclusion:
We can now begin to see why Sabbath observance is of the greatest significance and why our refusal to heed it is a great threat. In its practice, what we are finally doing is opening ourselves up to the happiness of God and letting God's intentions for menuha take precedence over our own ways. To refuse the Sabbath is to close the world in upon ourselves, by making it yield to our (often self-serving) desires and designs, and to cut ourselves off from God's presence and purpose. In our arrogant fantasies of dominating the whole creation, we forestall life and precipitate death. To forget or deny Sabbath is thus to withhold our lives from their most authentic purposes in God. It is to claim that our worrisome ways are better or count more than the intentions of God. It is to put ourselves at the center of creation -- the very definition of sinfulness -- rather than God's own delight.
In closing, these thoughts from Wirzba are entirely consistent with, and illustrative of, Question 1 of the Westminster Shorter Catechism:
Question 1: What is the chief end of man?
Answer: Man's chief end is to glorify God, and to enjoy him forever.
The Sabbath is given to humankind for the purpose of focusing on a single day each week upon our delight in God, his creation, and in the life to come from which the Sabbath is a reflection. It is the light of promise which we see on a night's distant horizon even when lost at sea, the olive branch from the foot of Noah's dove after days of incarcerating loneliness and isolation from his creation, the burning bush and cloud by day when we wander aimlessly among the giants of fear and intimidation.
Without it, we are bound to the same old patterns of creating our own way, with all its missteps, betrayals, heartaches, and failures. Observation of the Sabbath, one day in seven, is the formula by which God brings about our repentance, our confession, and ultimately our joy.