What is it about Shabbat that makes it so special? Why is it one of the most fundamental mitzvot in the Torah? The Zohar calls Shabbat,
yoma d'nishmata, the day of the soul. It is the ultimate pleasure of the soul, the highest expression of love between Hashem and the Jewish people. The sages say Shabbat is me'ein olam habah, a taste of the World to Come. The Ohr Hachaim in Shemot teaches that enjoying the Shabbat day is a privilege and a requirement. We have to experience the pleasure of Shabbat in this world to be able to move on higher to the full pleasure of the soul in olam habah.
The Rambam writes that if one keeps the Shabbat, it is as if one has kept the whole Torah. If one worships idols, it is as if one has desecrated the whole Torah. He rules that if a Jew violates the Shabbat purposely in public, he has desecrated his holiness as a Jew and has the halachic status of an idol worshiper. He is disqualified from giving testimony and cannot be a shochet (ritual slaughterer). Just as idol worship is a violation of a basic fundamental of the Torah, so is violating the Shabbat.
The sages say that the Shabbat contains more blessing and holiness than any other holy day. We also see that desecrating Shabbat is more severe than desecrating yom tov. If a Jew violates yom tov he is punished by kareit (his soul is cut off in this world and the next), while if he violates Shabbat he is punished by the death penalty of stoning. What about Shabbat makes it the holiest day of the year?
The Kobriner Rebbe notes that Shabbat is the fundamental connection between the Jewish people and Hashem. The Bereishit Rabbah says that when Hashem created the world He paired each day with a partner. Shabbat was left alone and so Hashem said, "The Jewish people will be your partner in marriage."
The Zohar writes that the 613 mitzvot help the soul maintain its holiness in a world of evil and defilement. The Torah is a roadmap showing us the way to traverse through the obstacles of this world so that the soul can eventually return to a higher place in heaven. Shabbat is the most potent way for the soul to tap into its holiness. When a Jew keeps Shabbat he connects to the holy light of the Creator that joins the soul to its original root under the throne of Hashem in heaven. For six days the soul struggles in a dark, evil, world filled with challenges. On Shabbat, the soul gains new energy for the coming week. The prophet Yeshaya said, "Az titanag al Hashem." The pleasure of Shabbat is being with Hashem, holding His hand, and basking in His embrace. The Ramchal says this is the goal of life. Man must navigate the maze of life and rediscover Hashem.
The Baal Shem Tov says deveikut Hashem is not meant to be reached in the World to Come. The pleasure of cleaving to Hashem can be experienced in this world on Shabbat. The Rambam says those who keep Shabbat get their reward in this world. It is the pleasure of being with Hashem experienced through the neshama yeteirah, the extra soul, that we get on Shabbat.
The Netivot Shalom writes an inspiring thought from the Avnei Nezer based on the Avudraham. On all the holidays, Shachrit, Mincha, and Maariv share the same basic prayer format. However, on Shabbat each of the three prayers are different. This is because Shabbat represents the marriage of the Jewish people with the seventh day.
The Jewish marriage has three levels. The first stage is kidushin, when the groom gives the bride a ring. The second level is nesuin, when he brings her into his domain. The third stage is yichud, when they merge into one entity. Similarly, Shabbat and Klal Yisrael are joined in a holy sanctified marriage that involves three stages. Friday night is kedushin. In Maariv we say, "Ata kedashta," You created a holy relationship. In Shachrit we advance to the next level of nesuin when we become one family unit. In Mincha we reach the final stage. The Zohar calls it rava d'rava, the deepest most profound love. We say, "Ata echad," You are one. The most joyous day of the week is Shabbat when the Jewish people, the groom, unite with the Shechina, the Shabbat bride.
Shabbat is the fusion between Hashem and Israel. Therefore, if a Jew violates the day, it is as if he cuts off his connection to the Almighty, as if he breaks the marriage contract and divorces from Hashem. To some extent, someone who violates Shabbat damages his holiness as a Jew and loses some of his Jewishness. But there is a road back. If he repents and observes Shabbat again, he can remarry Hashem and come back to full Judaism.
There is significance to the communal aspect of Shabbat. The Netivot Shalom points out that the gemara says, knesset Yisrael, the collective of Israel will be the marriage partner of Shabbat. Whereas an individual Jew can marry out of his religion and be lost to his nation, the Jewish people as an entity can never break its connection to Hashem. Hashem and Israel are married forever. The Almighty promised that He would always stay connected to us. When we keep Shabbat it's not only the individual keeping it, but the nation who can never be severed from Hashem or Shabbat.
This explains why the Netivot Shalom places great importance on joining a communal gathering to celebrate Shabbat. The beauty of Kabalat Shabbat reaches its peak as communities of voices sing Lecha Dodi together. On Shabbat day, we have the communal mitzvah of reading the Torah. Jewish law even allows a mourner to come to shul on Shabbat because it is through the community of Israel that we can connect to Hashem. The collective soul of nishmat Yisrael can never be defiled. It's above time and place and comes from a world where there are no sins.
Shabbat is the connection of the soul of Knesset Yisrael with the holy spirit of Hashem that comes into the world on the seventh day. We say in davening, "V'yanuchu bo kol Yisrael." The national soul rests on Shabbat. The Kozhnitzer Maggid and the Noam Elimelech taught that the union of love of the Jewish people on Shabbat is a collective experience, more than it is an individual experience. This is why if someone violates the Shabbat he is cut off in a certain sense from the Jewish nation. May we merit to experience the true sweetness and tranquility of Shabbat, the taste of Gan Eden, that is truly Shabbat.