The altar in the courtyard of the Mikdash should always have a fire burning. What does this symbolize? To understand this we must examine the nature of fire and see how it differs from the other three elements of wind, water, and earth.
The element of fire when it comes in contact with all matter which is flammable, transforms it into fire, thereby making fire the common denominator of everything that is burned. Fire needs matter in order for it to exist. Therefore the fire that we see now and in the next second are two different fires and existences. With new matter a new fire is created every second which feeds the fire with a new life.
With this we can understand the Medrash that says concerning Avraham Avinu ראה בירה דולקת ושאל מי בעל הבירה וענה ה' אני בעל הבירה
Avraham saw the world as a castle on fire and asked, who is the owner of this burning castle? Hashem turned to him and answered I am the owner and I command you with the mitzvah of Lech Lecha. The world being described by Avraham as one "on fire" conveys that it possesses a common denominator and thread and that is G-dliness. Avraham was therefore asking Hashem the source of everything to reveal Himself.
If one looks at nature alone, he will see separate details and different existences such as trees, rocks, people, sun, creatures, bugs, soil, water, insects etc. These individuals seem disconnected from each other. Yet science tells us that all these different eco systems, environments, and organisms, interact with each other. Not only do they interact but they all share a common microscopic sub atomic energy particles that gives them their existence. However, examining even further deeper this energy that sustains them is the most common basic denominator of every particle of the universe and that is Hashem's will that supports its life.
What Avraham realized and contacted, was the basic life energy that is shared by every existence and that is Hashem. This is described with the element of fire for it alone transforms all matter into the basic manifestation of Hashem's desire.
The Torah is also described as אש דת a religion of fire. This is understood in the light of above. Because the Chazal tell us הסתכל באורייתא וברא עלמא the Torah was the blueprints through which the world was created. Hence the wisdom of Hashem the Torah is the roots and origin of all life and matter in the universe. Therefore it is compared to fire – the בירה דולקת .
Secondly, as we found in the nature of fire, every moment there is a new existence of fire for the old fire has already terminated by consuming the matter it contacts. This teaches that not only does the world have one theme and common goal but that it also is sustained every second anew by the will of Hashem. The only reality is a new reality every mini second as we say in davening מחדש בכל יום תמיד מעשה בראשית.
During the six days of the week we describe the creation as מה רבו מעשיך ה' how plentiful and varied is Your creation. However, on Shabbos we say מה גדלו מעשיך ה' how big and connected is Your creation. During the weekdays we talk about the creation through the lens of multiplicities in a horizontal sense but on Shabbos we realize that the universe is a מגדל a tower with each part connected to the other with perfection unified by one purpose and goal. These two perceptions correlate to the description of Yaakov and Aisav concerning their worldly possessions. Aisav described them as יש לי רב I have plenty and a lot of it. The more I possess the greater the more separated and unrelated objects I have. Yaakov in contrast says יש לי כל I have everything. This is because Yaakov doesn't live with the exterior nature of the world, but rather with the life source heart beat which lies under the façade – with Hashem. When one connects and interacts with Hashem, he possesses "everything" because Hashem is infinite and the embodiment of everything. Rav Moshe Shapiro ztl wrote there is nothing that opposes the concept of רב more that the element of fire. And there is nothing that can transform רב into כל more than fire.
The altar in the Beis Hamikdash was situated at the center and source of the earth. The eternal fire on the mizbaiach symbolizes the sacrifice with at one must live in order to correlate his life with the perception and vision of כל and מה גדלו מעשיך , the opposite of רב and מה רבו מעשיך . The Menorah had a fire that burned daily. On the altar of spices the ketores was burned daily. The Shulchan had the lechem hapanim which its bread were steaming hot for the entire week. The Aron contained the Luchos the אש דת written with black fire on white fire. All this was a constant reminder that the life of an איש and אשה together in this world is to be on "fire" with the love of Hashem seeing the world of Hashem יה through the element of אש.
Shabbos aids and directs one to focus on their mission in life. The gematriah of בירה דולקת of Avraham is .יום שבת עה"כ Another gematriah that portrays the theme in our mamar is רבו מעשיך כל with the three words and כולל equal שבת. It is the Shabbos that transforms the רבו מעשיך of the week into כל. This is hinted in the gematriah of מה גדלו with its inner letters מ"מ ה"ה גימ"ל דלי"ת למ"ד ו"ו equals שבת עה"כ .
The Torah prohibits the kindling of fire on Shabbos לא תבערו אש בכל מושבותיכם ביום השבת. Why is this particular מלאכה out of the 39 pointed out? We suggest Shabbos is the day upon which its essence brings about the realization of בירה דולקת . Shabbos lights up the world with a heavenly fire which thereby makes it unnecessary for one to kindle on this holy day a physical one.
Wishing everyone a Guten Tamid אש תוקד על המזבח תמיד