In one of his shiurim on Chanukah (listen also to this shiur on the whole month of Kislev), Rabbi Paltiel explains that time is also a creation. Besides the time that is bound to space (which Einstein’s theories of relativity talk about), there is a more general, “background” time. Every moment of this time has its unique spiritual energy — Sunday has one type of energy, Monday another, etc.
This explains why certain holidays in Jewish history came and went, and other holidays remained. The particular day on which a particular holiday happened had its unique spiritual energy. The holidays with “universal” spiritual energies are still celebrated by Jews. For instance, the 15th of Nissan (the day when Jews left Egypt) had an energy of liberation, redemption from slavery, overcoming of one’s limitations and so on. This is why Pesach is celebrated throughout generations — not (only) to commemorate the leaving of Egypt, but mainly because the day itself is liberating; the same spiritual energy that allowed Jews to leave Egypt many years ago on this day appears again every year.
This applies to any holy day on Jewish calendar. On Rosh HaShana (New Year), the source of energy that allows the world to exist is renewed. By celebrating Rosh HaShana, we are celebrating literal rebirth of the Universe.
Shabbos is not merely a day to commemorate the fact that G-d “rested” (i.e., did not create the world actively); on this day, the stretch of time itself (and as a result, the world that exists in this time) is holy. The same mode of creation that was during the first Shabbos — through “thought” as opposed to “speech” — happens every Shabbos. It is as if on Shabbos we did not exist “outside” of Hashem, but inside His “mind”.
Rabbi Paltiel gives another example. In Sha’alos veTeshuvos min haShomayim (“Questions and Answers from Heaven”), a book in which halachic questions are asked “beyond the Curtain” and answers are recorded, at the end of one such teshuva, it is written: “Today is 19th of Kislev, Tuesday, and it is a day for celebration”. For a thousand years it was not known why 19th of Kislev was a happy day — until 1799, when on a Tuesday, 19th of Kislev, the first Rebbe of Chabad Chassidus, R’ Shneur Zalman of Lyadi (“Alter Rebbe”) was released from prison. This day became known as “New Year of Chassidus”, and it is generally recognized amongst Chabad Chassidim as a day instrumental for dissemination for Chabad Chassidus, which is a recipe for bringing Mashiach.
Yud-Tes Kislev is a lot bigger than Chabad. It is not New Year of Chassidus Chabad; it is New Year of Chassidus. In Yud-Tes Kislev lies spiritual victory of Baal Shem Tov. Baal Shem Tov was a special soul that came from heavens to introduce new, special type of Judaism, and it was being judged. [...] And the miracle of Yud-Tes Kislev effected not just Chabad Chassidim, but all Jews. [Listen on for explanation.]The same is true regarding Chanukah. The day of 25th of Kislev has the special spiritual energy of renewal and dedication of Beis HaMikdosh. When the Mishkan was built, it was ready to be dedicated on the 25th of Kislev. Moses was told by G-d to wait until Adar, but the energy of this day revealed itself when it came time (on the same day) to renew and rededicate Beis HaMikdosh after victory over Greeks.
So, it is true that we celebrate the historical occurence of each holiday, but this occurence is but a keili, a vessel for the spiritual energy behind the occurence. We are really celebrating the spiritual occurence of a particular day (that is happening on that day), but since we live in the physical world and cannot “grasp” the spiritual events in their purity (they are beyond this world) — nor should we do this, because the ultimate purpose of creation is making a dwelling place for G-d in this, physical world, — we “dress” the spiritual energy of a particular day in the “vessel” of a particular holiday, with its history, customs, special prayers, symbolism, etc.
That is why Purim, for instance, could be meaningful even for Jews in the middle of Holocaust. While the historical relevance of this holiday was seemingly distant and reversed by contemporary events, the spiritual relevance (Purim is higher that Yom Kipur, as the Lubavitcher Rebbe explains in one of his ma’amorim) was nevertheless there.
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This brings me to the question often asked about the “reason” of mitzvos. I will give a relatively obscure example. At the end of having a meal, before saying the main after-blessing for the meal, it is customary to wash one’s fingertips and pass the fingers over one’s lips. Men do this (usually, using a special cup and plate that is passed around the table); women do not. The explanation given on a nigleh (“revealed” or legal) level is that this custom was instituted to protect someone who had just eaten from the salts present in the food that may be harmful for one’s skin.
The question why this customs does not apply to women has several answers. One of them is that traditionally, women were involved with preparing food and therefore washed their hands anyway. Another is that the act of publicly washing one’s hands at the table is an act of doing something normally private in public, with the table’s attention drawn to oneself. Because privacy is more important for women than for men, it is generally recognized to be improper for the former to participate in attention-drawing events (which includes other activities, in which women normally do not participate, such as holding a public office, being a Rav, getting an aliyah, etc.).
Today, if we see in this custom nothing but a medical warning, it may seem somewhat irrelevant, to say the least. It may be surprising why this custom survived, while other, seemingly more important customs of past did not. The same logic that applies to holidays, however, applies to customs and mitzvos. They have both physical (historical, ritual, pragmatic) and spiritual dimension. The former is but a vessel for holding the latter.
Indeed, regarding washing of one’s fingertips after the meal, we find in the commentaries of AriZal (Rabbi Itzchok Luria, the founder of the most comprehensive contemporary system of Kabbala we have today — on which Chabad Chassidus is based, by the way) that through washing of our fingertips after the meal, we dispell the forces of klipah (spiritual impurity) that may have been attracted to us (similar to how the same forces are attracted to our body during our sleep and linger in the fingertips after we wake up, making it neccessary for us to wash them). Indeed, this is the kavana (conscious intent) one needs to have while washing one’s hands after the meal — to get rid of these forces of impurity.
So, why don’t women wash their fingertips? Apparently, because the forces of impurity do not affect them in this case. How do we know this? Because women are not required halachically to wash their fingertips after a meal. The most important lesson that Chabad Chassidus teaches us is: we must realize that ein od milvado — there is nothing but G-d. There is absolute unity of G-d with His creation, both space and time. All events happen in time and in space when they are supposed to happen according to the grand design of creation. Spiritual at all times is connected to the physical, both in historical events and in Torah.
Therefore, if — for whatever historical reasons! — women were not obligated to wash their fingertips at the time that this custom was instituted, it must mean that whatever the spiritual dimension of this custom is, it did not apply to women but applied to men. Even if nowadays the particular physical causes of this difference (and the reason for the custom itself) no longer apply, their spiritual aspects still do, making it necessary for us to honor the custom.