Rashi begins his commentary on Parshas Behar with the famous question of "mah inyan shemitah eitzel Har Sinai?" His question remains unanswered when we informs us that it comes to teach that as the laws of Shmitah were given at Sinai with all it nuances and intricacies, similarly all of the particulars of all the mitzvos were given at Sinai. The question remains; could not any other mitzvah have served in this capacity, teaching that all its parts were taught at Sinai?
Rav Yosef Salant zt"l in his Be'er Yosef suggests a fascinating answer. As the Yerushalmi notes (relating to (Shemos 6:13) "vayetzaveim el Bnei Yisroel") regarding Hashem's telling Moshe to give Bnei Yisroel the mitzvah of shiluach avadim (to free their slaves they would have in the future), that it is so difficult for a master to free a salve. It was only that they were in Mitzrayim, feeling the plight of slavery, that they could accept upon themselves this mitzvah at that time. Similarly, Behar Sinai, refers to the very special environment the preceded Matan Torah. The Gemarah (Shabbos 146a) teaches that when the Satan beguiled Chava to eat of the forbidden fruit in Gan Eden, he injected in her a zuhamah - an impurity, which among other things manifested itself in doubt, specifically doubting the oneness of Hashem and the complete authenticity of his Torah. This zuhamah was purged and expunged from them during the six day encampment at Sinai (from Rosh Chodesh Sivan to the 6th of Sivan). Thus the special introduction of Shmitah beign given at Har Sinai is to be understood as follows. The mitzvah of Shmitah is an incredibly difficult mitzvah (see Vayikra Rabbah, beginning of Parshas Vayikra). To relinquish ownership of your land, to remove the "No Trespassing" sign, could only happen at Sinai, after being purged from the zuhamah.
The Chinuch (Mitzvah 84) writes that the mitzvah of Shmitah, in addition to serving as a reminder to the Jewish nation that Hashem created the world in six days and rested on the seventh (and hence we work six units and rest on the seventh, both in the realm of days and years), gives us an additional opportunity to emulate Hashem (v'halachta b'drachav- Devorim 28:9). Just as Hashem bestows in His generosity blessings upon man and does not ask anything in return for Himself[1], the mitzvah of Shmitah trains the Jew to be altruistic, to open his field to all, rich and poor alike, without any strings attached or immediate benefit for the farmer.
Similarly, in Parhas Behar (Vayikra 25:36) the Torah says "do not take from him interest and increase; you shall fear your G-d and let your brother live with you." At first glance it is most difficult to understand why it is forbidden to take interest on a loan. To begin with, the lender will charge less interest than the bank. In addition, the borrower is only too happy to pay. Thus, just as one can forgo and cancel a debt owed to him, wherein lies the sin if the borrower is willing and happy to pay interest? The answer, explains Rav Chaim Shmuelevitz zt"l is that we are not dealing with a mitzvah bein adam lachaveiro (an interpersonal mitzvah), butrather bein adam laMakom (between man and G-d). if the lender charges interest, he is benefiting from the plight and circumstances of his neighbor in need. He is personally gaining, literally, at the expense of another. Note that prior to mattan Torah we would have called lending on interest a chesed. Independent of what you take for yourself, you have helped the next one. However, Behar Sinai we are taught a higher level of giving, one of n'divus, i.e. emulating Hashem by assisting without any personal benefit whatsoever.
Case in point: a neighbor assists another in a fashion that is clear to all. It involved time, effort, and money. After the kindness was performed, the recipient did not even say "Thank you" for the neighbor's help. The neighbor, the practitioner of the kindness, is appalled - "imagine, he did not even say 'thank you'!" An honest evaluation is to take place. If the good neighbor is troubled by the flaw in the recipient's character, that is understandable and acceptable. If, however, on a personal note he is slighted, hurt, and offended, then this can serve as the barometer as to the true measure and degree of altruism in his chesed. If the lack of appreciation on the part of the recipient disturbs the neighbor personally, it reveals a lack of total altruism in his service. He has yet to achieve, and must further aspire to, v'halachta b'drachav, emulating the ways of Hashem, which includes assisting without any strings attached.
This ennobling character trait of altruism is not only taught by specific mitzvos, such as shmitah and the prohibition or ribis, in Parshas Behar, but it is also culled from the holy city of Yerushalayim. It is well known that the Torah imposes a vacation on the Jewish farmer in the first, second, fourth and fifth years of the shmita cycle. After giving ten percent of his crop to the Levi, the land owner is to take and additional ten percent (either of the actual produce or the monetary equivalent thereof which is then used to purchase food in Yerushalayim), and eat it in Yerushalayim (Devorim 14:22-27). Tosafos (Bava Basra 21a) writes that the experience of observing the kohanim officiate in the Beis Hamikdash contributed and inspired the visitor to greater spirituality, as is says, "so that you will learn to fear Hashem, your G-d, all the days" (ibid 23).
In addition, commenting on the verse in Tehillim (48:3) "fairest of cities, joy of all the Earth" the Medrash Shemos Rabbah(52:5) understands David's description of Yerushalayim to refer not only to its physical beauty, but that in accordance with the teaching of Rabbi Yochanan - that there was a specific designated location where one did their personal financial accounting, outside the holy city proper. The balancing of one's checkbook, as important and practical for one's day to day operations, was of a personal nature. This was not to be done, ideally, in Yerushalayim. There, one's focus was to be on K'ir shechubra la yachdav - a city that is united and unites. A city of total altruism.
May our praying and pining for Yerushalayim further awaken within us these especially rich unique Jewish traits.
[1] The many mitzvos He asks us to observe using our resources are all for our good. For example, in the merit of giving a tenth of our produce we become wealthy, as Chazal explain the possuk "aser t'aser" - giving a tenth of our produce ("aser") so that you will become wealthy "t'aser").