Today, on Tisha B’Av—the ninth day of Av, this year commemorated on the tenth day of Av because the ninth is Shabbat, when mourning is forbidden—we mourn the destruction of the Holy Temple—Bet HaMikdash. This day commemorates the destruction of the First and Second Temples in Jerusalem. The First Temple was destroyed by the Babylonian king Nebuchadnezzar II, and Second Temple was destroyed by the Romans. Aside from its historical significance, why is the destruction of both Temples so tragic that it is mourned even today? What is the significance of the Temple in Jerusalem?
The Temple was a building where kohanim-priests offered sacrifices. The sages state that the Temple was a source of life for the Jewish people. This can be seen easily if we examine the parallels between the Temple and a living cell.
To understand the meaning of the Temple, we need go no further than the literal meaning of its name—Bet HaMikdash. Literally, Bet HaMikdash means the Holy House, referring to the Temple in Jerusalem. But why this name? Why not call it the Jerusalem Temple (as it is sometimes done in English) or Bet El (the House of G-d, as the patriarch Jacob called it)? Why is the emphasis on its holiness? To understand this, we must first understand the meaning of the word kadosh (“holy”).
What Is Holiness?
With apologies to mystics and romantics, the word kadosh has a very prosaic meaning—it simply means “separated.” Take, for example, the marriage ceremony, called in Hebrew kiddushin. It simply means “separated”—by this ceremony, the bride is separated from the pool of marriageable women, so that no one else can marry her. When the nation of Israel is called am kadosh, it simply means that it is a separate nation whose members may not intermarry with members of other nations. Even when we call G-d kadosh, we mean that He is separated from the world, which He utterly transcends. Thus, the additional meanings of “holy” or “sacred” are secondary to the plain meaning of “separated.”
With this understanding, we can translate Bet HaMikdash as a separate or isolated building. Its inner space is separated from the environment by its walls. Prosaic? Perhaps. But a deep meaning is hidden in this literal translation.
The Cell—the Quantum of Life
As mentioned earlier, the Temple was considered the source of life. The smallest unit of life—its quantum—is a cell. The very meaning of the word “cell” comes from the Latin word cellula, meaning “small room.” A major characteristic of a living cell is that it is surrounded by a semipermeable membrane that separates it from the environment. In this sense, every cell is kadosh, that is, separated. The reason such separation is necessary for life is this. In 1944, one of the founders of quantum mechanics, Erwin Schrödinger, defined life as that which resists decaying from order to disorder. Such resistance, however, would contradict the second law of thermodynamics, according to which entropy—a measure of chaos and disorder—always increases in a closed system. All things tend to decay, and disorder tends to increase—except in a living cell, which maintains homeostasis (a steady state) by working hard to defeat the decay. That is only possible in an isolated system. A cell decreases the entropy inside the cellular wall by increasing the entropy in the outside environment. This may sound like a lot of work for a cell. But this is exactly what every household refrigerator does—it cools the inside of the refrigerator by extracting heat and releasing it into the environment. It cools the food at the expense of heating the kitchen. A living cell extracts order from the environment so as to maintain the highly ordered state of homeostasis inside the cell by increasing disorder (entropy) outside. To accomplish this, it is critical for the cell to maintain a semi-isolated structure, where energy and nutrients are extracted from the environment and the byproducts of cellular metabolism (that is, waste) and heat are expelled into the environment.
The structural parallel between the Temple and a living cell is beginning to emerge. First, let us note that the walls of the Temple also served as a “semipermeable membrane”—animals, flour, olive oil, and wine used for sacrifices were brought in, whereas the smoke of burning sacrifices and the ashes were taken out.
Every cell contains a cytoskeleton, a series of interior fibers that connect the cell nucleus to the cell membrane or wall. The cytoskeleton supports and keeps in place the various organelles within the cell. This is parallel to the interior architecture of the Temple with its various rooms and areas designated for different purposes.
All eukaryotic cells (which include all animals, plants, fungi, and protists) contain a nucleus. The Temple too contained a nucleus—the Kadosh HaKadoshim (the “Holy of Holies”). In a cell, the nucleus contains double-stranded DNA. The Holy of Holies contained the two Tablets upon which the Ten Commandments were written. Cellular DNA contains the genetic code. The Ten Commandments written on the Tablets is the genetic code of Judaism. Just as DNA is isolated from the cytoplasm—the intracellular fluid—by an internal membrane, so too the Tablets are isolated by the walls of the aron—the box in which they are contained.
A cell has a number of functional units separated by membranes that are called organelles. The nucleus is one such organelle, mitochondria are other very important organelles. Mitochondria is a power plant or a battery supplying the energy to the cell. In the Temple, the altar on which sacrifices were burned could be considered structurally parallel to cellular mitochondria, although this parallel is looser than others listed above. There are many other organelles in a eukaryotic cell. Similarly, in the Temple, there is a number of other units called kelim, which included a Menorah, an incense altar, and showbread table.
I do not claim that every structure and every function of a living cell has its counterpart in a Temple. However, the main purposes of both are parallel in the following sense. The Kabbalah teaches that this universe was preceded (in a causal, not temporal sense) by another universe called Tohu—the universe of Chaos. The sefirot of the universe of Tohu shattered and fell into our universe—the universe of Tikkun (“rectification”). The shards of the shattered vessels of Tohu represent chaos and decay. Our purpose is to reverse the decay by extracting the sparks of holiness that fell from the universe of Tohu and rectify the shattered vessels. This is what was done in the Temple through the burning of sacrifices. Similarly, in a living cell, energy is spent to reverse the decay and to maintain the highly ordered state of equilibrium so necessary for life.
As we see, the statement of the sages that the Temple was the source of life was far from waxing poetics—it was a precise statement which we can now back up by the structural parallels with a living cell. As a metaphor for a living cell, on a mystical level, Bet HaMikdash was seen as the source of spiritual life.
This may help us to understand a curious biblical verse:
Make me a Sanctuary, and I will dwell among them. (Exodus 25:8)
In the Chasidic philosophy of Chabad, this verse is usually interpreted to mean that G-d promises to dwell in every Jewish person in a form of Nefesh Elokit—the divine soul. However, this does not explain any connection with the first part of the verse—what does this have to do with constructing the Sanctuary? Perhaps we can explain it by suggesting that “I” in this verse stands for the teleological principle—the purpose. It is as if G-d told Moses that just as the Sanctuary is a metaphor for a living soul, G-d endows every living cell with the purpose of fighting decay and maintaining order to promote life.
Now, we can also understand the enormity of the tragedy of the destruction of the Temple. Living cells don’t just stop functioning. As they grow older, cells may become senescent and can malfunction. But they nevertheless remain alive so long as they maintain the integrity of their cellular wall. The breach of the cellular wall defines the death of the cell. Similarly, the Second Temple in Jerusalem was in a somewhat dysfunctional state for a while prior to its destruction. Some High Priests were heretics (Sadducees), some were corrupt and bought their positions as High Priests from the Romans. At some point during the siege, the sacrifices stopped. But, so long as the Temple stood, there was hope. Once the walls of the Temple were breached, the Temple ceased to exist. The spiritual source of our life died, as it were. This is what defines the essence of Galut—the exile. This is why Jews cry every Tisha B’Av and pray for the building of the Third Temple. May it happen speedily in our days!
 This could be readily seen in the Biblical prohibition against using an ax or other metal tools in making the misbe’ach (the altar). The stated reason is that it is inappropriate to use an ax, a weapon of war, or, generally, any metal that could be used to make weapons of war intended to cause death, in making an altar, which is a source of life. See Mishnah, Midot 3:4.
 Genesis 28:18, 35:7.
 This is a key concept of the Lurianic Kabbalah called Shevirat HaKelim—the Shattering of the Vessels.