Sefer Yetzira speaks of three dimensions: Olam, Shanah, and Nefesh. Olam literally means “world” and signifies space. Shanah literally means “year” and signifies the dimension of time. Nefesh literally means “soul” and signifies the spiritual dimension. In another place, recognizing the space itself is three dimensional, Sefer Yetzira speaks of five-dimensional space which is a Minkowski spacetime with an addition of the fifth spiritual dimension. This construct is very similar to the Kaluza-Klein five-dimensional generalization of the General Theory of Relativity (a theory that is near and dear to my heart, because, unaware of its existence, I independently rediscovered it as a teenager.) Kaluza-Klein, first forgotten, is now experiencing a revival as a special case of the string theory.
In every one of these dimensions, G‑d created the domain of holy and the domain of profane; and He commanded us to separate between the two. This is part of being a holy nation—Am Kadosh, as kadosh literally means “separated.”
In the domain of space, we have reshut hayahid—the domain of one, and reshut harabim—the domain of many. The former signifies the One above, and the latter signifies the multiplicity of the mundane world. We separate between the two by affixing mezuzot on the doors of our houses creating a line of demarcation between the domain of one and the domain of many and separating the sanctity of a Jewish home and the mundane world outside it.
In the domain of time, we have Shabbat, which is the domain of holiness. We also have weekdays, which are mundane. We sanctify Shabbat by making a Kiddush at the start of the Shabbat and separate it from mundane weekdays by making Havdala at the conclusion of Shabbat.
In the dimension of spirituality, G‑d chose the nation of Israel and made it holy. “You shall be holy because I am holy.” (Lev. 19:2) The separation between the Jews and other nations is expressed in the prohibition of intermarriage and the Brit Mila—circumcision—the sign of the Holy Covenant, which symbolizes this line of demarcation.
Thus far is explained in Kabbalah and Chasidic philosophy. I would like to suggest that each of these dimensions has, in turn, two subdimensions—external and internal—hitzoniut and pnimiut.
In physics, we also have concepts of external and internal aspects. For example, we have external symmetries, such as translational symmetry (that states that all laws of physics are valid in every point of space) and the corresponding law of momentum conservation, or time symmetry (that states that all laws of physics are valid every moment of time) and the corresponding law of energy conservation. But then, we have internal symmetries, such as the spin of elementary particles; charm, color, and the strangeness of quarks and their corresponded conservation laws. I think, similar inner symmetries exist in the Torah.
In the domain of space, we have mezuzot separating between the domain of one from the domain of many. However, this is the external aspect of space. Recall that mezuzot should be affixed not only at the front door, but on every doorpost inside the house with mezuzot separating one room from another room. The reason for this is that each room has its own unique purpose and mezuzah sublimates and dedicates this purpose to the service of G‑d. This is the inner aspect of space.
In the dimension of time, we have Shabbat as the domain of Holiness. However, the book of Zohar speaks of two Shabbats—Shabat Eliyon (Higher Shabbat) and Shabbat Tachton (Lower Shabbat). The lower Shabbat is the regular Shabbat that we celebrate every seventh day. The higher Shabbat is celebrated in the higher worlds, when we fulfill the will of G‑d. That is why Mishnah calls Pesach a “Shabbat” (see my essay on Passover). This higher Shabbat is the inner Shabbat, whereas the lower Shabbat is the external aspect of Shabbat.
In the domain of spirituality, we have Brit Mila. However, physical circumcision is the external aspect of Brit Mila. There is also circumcision of the heart, which will be attained with the coming of Mashiach (Messiah). In Chabad communities, it is customary for the father to recite at the brit the ma’amar of the Admur Hazaken (the Alter Rebbe, the first Lubavitcher Rebbe), which discusses the circumcision of the heart. This is the inner aspect of spirituality.
Tonight is Yom Kippur. When the Holy Temple stood in Jerusalem, on the day of Yom Kippur, the three dimensions—Shanah, Makom, Nefesh—converged together: on the holiest day of the year (Yom Kippur), the holiest soul (High Priest-Kohen Gadol) would enter the holiest place (Holy of Holies—Kadosh Hakadoshim).
When the Third Temple, Bet HaMikdash HaShlishi, is rebuilt with the coming of Mashiach, not only three external dimensions will converge together but all internals dimensions as well (incidentally, bringing the total number of dimensions to ten—the same number of dimensions as in the string theory). May this happen immediately!