Several of the mitzvos mentioned in Parshas Re'eh, i.e. the mitzvos of shechita (ritual slaughtering), ma'aser sheini (secondary tithes), and aliyah l'regel (tri-annual pilgrimage to Jerusalem) reflect a fundamental change that will occur in the Jewish people upon their arrival in Eretz Yisroel. During the forty years in the desert, the focus of the Jewish people was the Mishkan (tabernacle) to which everyone had easy access. After entering Eretz Yisroel the spiritual center for the Jewish people, would be found first in the Mishkan (Tabernacle) in Shilo, and eventually in the Beis Hamikdosh (Temple) in Jerusalem. However, due to the size of the land that Benei Yisroel would inhabit, some people would find themselves at a distance from the spiritual center. The mitzvos of shechita, ma'aser sheini, and aliyah l'regel deal with this new reality and teach Benei Yisroel how to adjust appropriately.
The Torah introduces the mitzva of shechita (Devarim 12) by stating that it is dependant upon our living far from the Beis HaMikdosh. Rashi quotes the opinion from the Talmud in Chullin that the slaughtering of an animal for personal use that would not be offered as a korban was only permitted after the entry of the Jewish people into Eretz Yisroel. When Benei Yisroel lived close to the Mishkan in the desert, it was only permissible to eat meat in the context of a korban. To eat non-sacrificial meat (basar chullin) was only permitted by the Torah because it was no longer feasible to always travel to Jerusalem when one wanted to eat meat. The Jew, who for forty years in the desert, never ate meat outside of the context of holiness found himself in a dangerous situation. He was far from the Mishkan, and was no longer subject to the strict laws governing ritual impurity for food. There existed the possibility that he would partake of his meat with no semblance of sanctity. Therefore, the Torah emphasized how to live in holiness even miles away from the source of holiness itself. The animal had to be slaughtered in the precise manner a sacrifice was slaughtered. Blood could not be eaten because blood is reserved for the mizbeach (alter). Although the Jew may be geographically distant from Jerusalem, he was reminded that he still must live in a way which meets the standards that Jerusalem represents.
In a similar vein, the mitzva of bringing ma'aser sheini to Jerusalem, and eating it there in a state of holiness and purity, became difficult to perform as the Jewish people became spread out throughout Eretz Yisroel. Ideally, a farmer would travel to Jerusalem, several times a year, bringing the fruit of his harvest. Practically, this could not be fulfilled due to the difficulty of transporting produce over the long distance to Jerusalem. The Torah teaches us that under these circumstances there was an alternative. The produce could be redeemed for money, and eventually, when it was feasible, the farmer could bring the coins to Jerusalem to purchase food. (The coins must be guarded lest they be used for another purpose.) This food, elevated to the equivalent of ma'aser sheini, was then eaten in a state of sanctity and purity thereby enabling each Jew to experience the sanctity of Jerusalem even if he can not travel there at the original time. Even the distant farmer had to preserve the sanctity of his fruit until he redeemed them.
Parshas Re'eh concludes with the mitzva of the three time a year aliyah l'regel. When the entire Jewish people camped around the Mishkan there was no need for a special visit to the Mishkan on the occasion of Peshach, Shavuos, and Sukkos. After the Jewish people spread throughout Eretz Yisroel and it was no longer feasible to come to the Beis HaMikdosh on a regular basis, the mitzva of aliya l'regel became the means to retaining a relationship to Jerusalem and all that it represented.
Visiting the Beis HaMikdosh was the focal point of the entire year, even when it could not be done as often as it ideally should have been. The yomim tovim (Jewish holidays - Pesach, Shabuos, and Sukkos), the highlights of the Jewish calendar, would always be bound with the sanctity of Jerusalem. The preparation and the actual travel would always ensure that Jerusalem remained foremost in the mind of all Jews, even in the mind of those who are geographically distant from it.
Parshas Re'eh teaches us that our minds and hearts must constantly revolve around the kedusha and tahara that emanate from the Beis HaMikdosh in Jerusalem. Even if we find ourselves geographically distant from Jerusalem, our standards of behavior must always meet those appropriate to Jerusalem. Even if we are not yet privileged to perform the mitzvos of eating ma'aser sheini in Jerusalem and aliyah l'regel, let us face Jerusalem as we pray to Hakadosh Baruch Hu. May we merit to serve Him in the Beis HaMikdosh and may the spirit of kedusha and tahara emanate from Jerusalem to the entire world. "Ki mitziyon tetsei Torah u'dvar Hashem m'Yerushalayim" ("for Torah comes out from Zion, and the word of G-d from Jerusalem").