One of the prominent k'lei haMishkan, one that involved a weekly 'avoda, was the shulchan (table). 12 loaves of bread, the lechem hapanim, were placed on it in two rows of 6 which were exchanged every Shabbos for fresh ones. The original loaves were then consumed by the kohanim in the 'azara in accordance with all of the stringencies of the eating of other kodshei kodashim (holiest sacrifices). Several questions may be raised concerning this 'avoda. Why was it necessary for bread to be placed in the mishkan and later in the Beis haMikdash every week? The Talmud (Yoma 39) comments that when the kohanim ate the lechem haPanim, even one who received a minute amount would be full from it. What is the reason behind this particular miracle?
The Ramban, in his commentary to our Parsha, presents an answer to both of these questions. Ever since Hashem originally created the world, ex nihilo, yeish mei'ayin, all other Divine acts of creation and intervention take place yeish miyeish, starting with some matter and then modifying it or adding to it -- either in an overtly miraculous fashion or in a hidden way, utilizing the rules of "nature", in order to bring about Divinely desired effects in the world. The story of the woman, who, destitute and in debt, at the directive of Elisha, fills many jugs with oil from only one jug which she then sells to repay her creditor and sustain her family, serves as an example of this principle. When no more jugs were available, the flow of oil stopped. Hashem did not create more oil out of nothing for her (see M'lachim 2, Chapter 4), He only created more oil from the existing oil. So too, writes the Ramban, concerning Divinely granted sustenance in general, it "flows" through the Mishkan and later the Beis HaMikdash and specifically through the lechem hapanim of the shulchan to the rest of the world. The bread, so to speak, serves as the conduit for the Divine shefa, or blessing, and "multiplies" throughout the world. According to this principle, the degree of sustenance in the world when the Beis HaMikdash stood was much greater than the degree of bounty after its destruction. Megillas Eicha and the kinos on Tish'a B'av as well as the Musaf prayer of Yom Kippur all refer to this theme quite frequently. Similarly, the Mishna (Sota 48a) records the statement of R. Yehoshua: "From the day the Beis HaMikdash was destroyed, there is no day without a curse, the dew does not fall in a blessed way, and the delicious taste of fruit was removed." The immense bounty foretold in the times of the final redemption by the prophets would be a direct result of the reestablished window of Divine sustenance.
Based on this concept of the Ramban, we can suggest an explanation to what appears, at first glance, to be a cryptically arranged b'racha of the Birchat HaMazon. The blessing of Racheim begins with a plea to G-d to restore the Jewish people to their land, rebuild the Beis HaMikdash, and reestablish the Davidic dynasty. Then, the blessing switches to a series of requests for food and sustenance (r'einu, zuneinu, parn'seinu, v'chalk'leinu...), concluding again with a prayer for the rebuilding of Jerusalem. How are these two themes linked? Perhaps the connection is that we first ask Hashem to rebuild the Beis HaMikdash and, aware of its benefits in serving as the gateway through which our sustenance is channeled, we request that he sustain us more fully in that period of redemption. Or, it has been suggested, that, absent a Mikdash which contained this portal, we beg that Hashem still provide for us through the residual "trickle" of Divine blessing (see commentary of Iyun T'fila in Siddur Otzar HaTefillos).
The Mishkan/Mikdash is symbolic of 'avodas Hashem in general. It is the place of Man's rendevous with his Creator, a center for the reestablishment of his connection to Hashem and the reaffirmation of his recognition of G-d as the center of the entire universe. It is not surprising then that this place also serves as the gateway to Divine bounty. The Torah informs us time and time again that not only our eternal, everlasting destiny in the next world is determined by our loyalty to HaKadosh Baruch Hu and his Torah, but even our fate and material success in this world is largely determined by such devotion. The Divine flow of our necessities is commensurate with the extent that we intensify our 'avodas Hashem. One cannot help but marvel and appreciate the chasdei Hashem in our own era as reflected in how much material bounty there exists currently in the world. At the same time, we are acutely aware of the lack of sustenance for so many of our brethren and in many regions of the world at large. Chazal teach us that so much more awaits in the otz'ros haShamayim (Divine storehouses) if we rededicate ourselves to Divine service and specifically through the return of the Mikdash. May we merit that all of our needs, individually and communally, be provided by the Masbi'a l'chol chai ratzon (the One who satisfies all willingly) and, even more so, merit speedily the day when the Divine portal for blessing will be reestablished through the building of the third Beis HaMikdash.