When Adam was created, he entered a spiritually pure world. In a sin-free setting, Hashem's presence is palpable and it is quite comprehensible that one living in such an environment would be able to converse with the Creator Himself as was the case with Adam. Unfortunately, this utopia lasted only a number of hours. He sinned by eating from the eitz hada'as and thereby plunged the world into a spiritual darkness. This darkness culminated with the destruction of most of mankind during the flood.
Avraham Avinu began building a new world of spirituality. Seven generations later his offspring stood by Har Sinai and declared na'aseh v'nishma and thereby restored the world to its original state of spiritual purity. Once again those present at that time merited hearing words emanating from Hashem Himself. However, shortly thereafter the original course of events recurred: a sin was committed and it hurled the world downward into a spiritual abyss.
According to the Seforno, the building of theMishkan was meant to rectify this situation and create an edifice which would act as a substitute for the former world of purity. The Mishkan was in effect a microcosm of the universe. When Moshe Rabbeinu entered this abode which was untainted by sin, he immediately heard the voice of Hashem. Indeed, anyone who entered encountered numerous miracles that proclaimed Hashem's presence.
Chazal tell us (Shemos Rabba 34:1) that when Hashem instructed Moshe to build the Mishkan, Moshe wondered aloud: "His presence fills the entire universe and He is asking me to build an abode for Him?" Hashem responded, "I did not intend it to be as big as you think it should be. Erect twenty beams on the northern side, twenty beams on the southern side and eight beams on the western side. Moreover, I will descend and rest My Shechina within a space of a cubit by a cubit." Rav Wolbe (Daas Shlomo) quotes Rav Yeruchom Levovitz's explanation of Moshe's surprise. Moshe did not assume that Hashem intended to maintain His presence in the world and merely occupy an additional personal abode. Had this been the case then there would be no place for his question since such an endeavor would not necessitate a huge building. Rather, Moshe understood that Hashem was planning on removing His presence from the entire universe and dwelling solely in the Mishkan! Hashem responded with the concept of tzimtzum Ha'Shechina - He would condense His presence and limit it to a single square cubit!
Alas, the Mishkan and Beis Hamikdosh have been destroyed and Hashem's presence on earth is no longer felt. Do we have any hope of regaining His presence in a fashion similar to what was felt in the previous generations? Chazal (Brachos 8a) enlighten us and assert, "From the time that the Beis Hamiksosh was destroyed Hashem has no place in this world aside from the four cubits of halacha." We are left without a Mishkanand without any of its vessels, but Hashem still finds a way to condense and concentrate His presence i.e. on a person who delves into the Torah l'halacha.
Reb Naftoli Amsterdam once lamented to his Rebbi Reb Yisroel Salanter that he feels inadequate to properly serve Hashem. "If only I had the brilliant mind of theShaagas Aryeh, the passionate heart of the Yesod V'Shoresh Ha'Avodah and your sterling middos, then I would be able to properly serve Hashem!" Reb Yisroel Salanter replied, "Naftoli, with your mind, with your heart and with your middos you have the ability to be a trueoveid Hashem!" Rav Yeruchom Levovitz comments that Reb Yisroel Salanter was informing his disciple of just how far this idea of tzimtzum Ha'Shechina goes. Hashem will even condense His Shechina and rest it upon a person with limited intellectual abilities, a small heart and unpolished middos, as long as he serves Hashem with seriousness and wholesomeness. We have the ability to build a Mishkan. We do not even have to travel to Yerushalayim since the building is to take place in our own backyard. The most lucrative investment is the investment of time one spends in building himself into an abode for the Shechina!