The Leviim are singled out from the rest of the Jewish people to have a unique role. Unlike most of the Jewish people who would receive a share in Eretz Yisroel, the Leviim would not be involved in agricultural work. The Leviim would dedicate themselves to the service of Hashem and be supported by the other tribes. Although one becomes a Levi by birth, the Rambam in the end of Hilchos Shemittah V'yovel describes a different kind of Levi. Any person who decides to dedicate his life to Hashem and separate himself from worldly pursuits is a spiritual heir to the Leviim of old.
This second type of Levi spends his time in service of Hashem primarily through the study of Torah. How did the Rambam see in the individual who commits himself wholeheartedly to the study of Torah as continuing the legacy of the Leviim? The Leviim were involved in the service of the mishikan and later the beis hamikdash. How is the study of Torah a continuation of the beis hamikdash?
Although the avodas hamikdash was a primary task of the Leviim, there was another role they fulfilled. The sanherdin is described in Devarim as being comprised of Kohanim and Leviim. In the bracha that shevet Levi receives from Moshe Rabbeinu they are blessed to be the teachers of Torah as well as those who serve in the beis hamikdash.
This dual role of the Leviim stems from the dual role of the beis hamikdash itself. Although we usually associate the beis hamikdash with the offering of korbanos, there was another dimension to the beis hamikdash. The sanhderin sat in the beis hamikdash and the aron with the luchos was at its center. The Leviim guarded over both aspects of the beis hamikdash; they assisted the Kohanim in avodas hakorbanos and also were the teachers of Torah.
These two aspects of the beis hamikdash and the Leviim who watched over it complement each other. The beis hamikdash was the meeting point between Hashem and Bnai Yisroel. We reach out to Hashem through offering korbanos, and He reaches us by teaching us His Torah. The Leviim who assisted in the offering of korbanos and taught Torah enabled this bonding between Hashem and His people to occur.
Chazal teach us that after the beis hamikdash was destroyed, all Hashem has left in this world is the study of Torah. Even though we can no longer reach out to Hashem by offering korbanos, we can still come closer via Hashem sharing His Torah with us.
Although the role of a Levi as part of the avodas hakorbanos no longer exists, the role of a teacher of Torah endures. It is this role of the Levi that can be assumed by anyone. Anyone who decides to dedicate his life to the study and teaching of Torah is following in the footsteps of the Leviim. Through the study of Torah Hashem is able to reach out to us even in the temporary absence of the beis hamikdash. May we merit to see the rebuilding of the beis hamikdash and witness the return of "Kohanim la'avodasam u'Leviim l'shiram u'l'zimram" - the return of the Kohanim and Leviim to their service of Hashem and His people.